The following weapons are seen in the video game Counter-Strike: Source:
As is common for CS games, the weapons are mirrored in first person. However, it appears that this time the mirroring is an intentional homage to the original CS games rather than an accident from the animation process, as some of the weapons have correct markings on right-handed weapons (earlier games simply didn't have the power to support such high quality textures), suggesting that they were intentionally modeled as mirrored weapons.
The Glock 19 is called "9X19 Sidearm" in the game. Its in-game model is smaller than a Glock 17 or 18 and has a (textured) rail, indicating that the texture wants it to be a 3rd gen Glock. The model itself lacks the finger grooves (which are never seen anyway). It has the ability to fire not only in semi-automatic, but as well as 3-round burst fire mode. The Glock 17C was one of the first pistols added in beta 1 of the original Counter-Strike mod for the first Half-Life.
The factual inaccuracy comes in that the Glock 19 can fire only in semi-auto, and it can't be a Glock 18 because it lacks the fire-selector (which would be on the other side anyway, due to the mirrored model) and a real Glock 18 can only fire in semi and full-auto, no burst (no version of the Glock comes with a burst in fact). The gun itself holds (an incorrect) 20 rounds yet is underpowered compared to other handguns in the game. This gun is standard issue for Terrorists. This is more of a 'spray and pray' type of gun as it has very little recoil and reloading takes very little time. Although, this gun has a very large bullet spread when fired rapidly.
Heckler & Koch USP45 Tactical
The H&K USP45 Tactical comes with a suppressor and is standard issue for Counter-Terrorist. It can be fired just as fast as the FN Five-seveN and the G17, although it only has 12 rounds. Aiming at the chest/head will lead to a kill within 2-3 rounds. Used in conjunction with the "Maverick M4A1," "Schmidt Machine Pistol" and the sniper rifles to maintain stealth. Interestingly, the in game icon is that of a standard USP.
The SIG-Sauer P228, called the .228 Compact in the game, is a mid-range gun with moderate power and accuracy. It holds 13 rounds which are quite effective on Kevlar armour. This gun comes with no extra attachments or firing modes. It is chambered in-game as a .357 SIG model, as opposed to .40 S&W or 9mm Luger. Technically, that makes it a SIG-Sauer P229.
IMI/Magnum Research Desert Eagle Mark XIX
The Desert Eagle Mark XIX is renamed as the Night Hawk 50c in game (although the model files refer to it as the 'Deagle'). It's extremely powerful as far as handguns go but only carries seven rounds in a magazine. Good backup for aggressive snipers because of its high power. Also, while it is chambered in .50 AE in game (see screenshots), the pistol appears to have a fluted barrel, which would make it the .357 or the .44 magnum version of the Desert Eagle. It is odd that this gun would be in this game because no police or military forces have (or ever for that matter) used the Desert Eagle in any of its variants/calibers.
Fabrique Nationale Five-seveN
The FN Five-seveN, called the "ES Five-Seven" in the game, is fairly accurate but with a very low power. It holds 20 rounds and is capable of rapid fire if you tap the mouse fast enough. This gun is only available to Counter Terrorists. The in-game model suggests that this is the first-generation model that had the "P90 style" trigger guard and lack of an accessory rail (without aftermarket modifications). The slide serrations of the in-game model also suggest that this is a first-generation model.
Beretta 92G Elite II
The Beretta 92G Elite II is a dual-wielded weapon and is called the '.40 Dual Elite' in the game, despite being chambered for 9mm. The guns are only available to the Terrorist faction, where they are used as back up sidearms but are sometimes used as primary in the first three rounds. The guns themselves are more aesthetically pleasing weapons than the others and hold 15 rounds each. The guns are medium range, medium power and can take up to 4 rounds to kill. With there being 2 guns, reloading is slow and are the most expensive handguns in the game.
Benelli M3 Super 90
The pump-action-only version of the Benelli M3 Super 90 in CS called the 'Leone 12 Gauge Super'. It is a very underused weapon, which is very deadly up close. Like the M4 Super 90, it is best used in close quarters combat. The range, however, is short. Reloading is the same process with the M4, with the exception that the M3 can hold 8 rounds, compared with the M4's 7. One feature that is not included in the game, however, is the ability to switch from pump action to semi-automatic operation, which can be done with the real life counterpart. There is a bit of a goof when pumping the M3: The tip of the mounted flashlight remains stationary, but the shaft stretches out with the pump.
Benelli M4 Super 90
The Benelli M4 Super 90 is called the 'XM1014' in Counter-Strike. It is a rapid firing 12 gauge shotgun used by both Terrorists and Counter Terrorists. It's a semi-automatic (but fires so quickly it appears to be fully automatic) and is best utilized in close quarter combat, as it has a short range but is very powerful. As you'd expect from a shotgun, full reloading of 7 shells takes a long time. However, the gun can be reloaded quickly after 2-3 rounds.
The Steyr TMP is a rapid firing, short ranged weapon available only to the Counter Terrorists, named the 'Schmidt Machine Pistol' in game. It is a weak gun, but has a high rate of fire and can kill within 4 rounds at close range. It features a non removable silencer which takes the power from the rounds but makes it almost silent. Used in conjunction with the H&K USP45 Tactical to maintain stealth.
A neat detail is that the third-person animation had changed so that the player character is actually gripping on to the foregrip like in first-person. In earlier games, the TMP is held like a pistol in third person (despite gripping onto the foregrip in first person), with both hands on the magazine well.
The MAC-10 is a powerful but inaccurate terrorist weapon. Its short range, high power and fast rate of fire makes it a very underestimated weapon. It is one of the few weapons not to be mirrored in first person.
Heckler & Koch MP5N
The H&K MP5N is another highly used weapon in the game, due to its fast rate of fire, quick reloading and good accuracy. Not as powerful as the more expensive rifles, but for the early rounds it is a safe buy.
Heckler & Koch UMP45
The UMP45 offers high accuracy and range what makes this a more powerful parallel to the MP5N, but holding only 25 rounds and a very slow rate of fire makes this a gun that's only used by players who are experienced with it or who are new to the game and do not know about its drawbacks. The charging handle incorrectly locks back on its own before reloading. A goof exists in the weapon's model; it is shown set to "safe", yet somehow fires fully automatic.
Fabrique Nationale P90
The 50-round magazine size of the FN P90 gives an advantage to the other sub machine guns featured. The gun's medium-short range and medium power makes this a great close quarter action gun. In its specs, it inaccurately lists that it uses .338 Lapua Magnum rounds, while in reality it shoots a 5.7mm round (This has since been corrected in an update).
Rifles / Carbines
IMI Galil ARM
The Galil ARM, called the "IDF Defender" in-game, is another gun which is considered a safe buy when money is an issue. Its 35-round magazine gives the player an extra edge when in an intense battle. The weapon has a medium range and less power than other rifles (such as the AK-47). Unlike the AK-47, the Galil's recoil can be more controllable and spraying a little more accurate. This gun is available to Terrorists only. The Galil in the game is the ARM variant as noted by its carry handle, heavy barrel, bipod and square-shaped hand guard. For some odd reason, it is shown with a maximum ammo count of 90 rounds, despite using a 35 round magazine. This would mean that the weapon comes with two full magazines and a 25 round magazine rather than than three full magazines totaling 105 rounds.
GIAT FAMAS F1
The FAMAS F1 is a low cost rifle for the Counter Terrorist. It is fairly cheap to buy, with an accurate 3-round burst fire and medium power. When used in full auto mode, the gun is fairly inaccurate, with the gun better used in close quarter combat. Despite having a 25 round magazine, it's max ammo capacity is 90 rounds. This translates to three full magazines and a 15 round magazine.
Appears as the "CV-47" in the game. The AK-47 can shoot through very thin walls and doors and is seen as a safe buy due to its cheap and effective build. It is standard issue (if you have the correct funds) for all terrorists. The gun has a very large bullet spread when firing full auto, but is almost pinpoint accurate when firing single shots.
The M4A1 Carbine (referred to in game as the "Maverick M4A1") is the most used weapon in the game and is only available to Counter Terrorists. The gun has an optional sound suppressor which decreases the power a little. Overall, some regard it as the best weapon in the game due to its high power and accuracy. Burst firing allows the gun to reach a long distance. The gun is very effective when running and shooting, offering well balanced characteristics with controllable recoil. Used in conjunction with the H&K USP .45 ACP Tactical to maintain stealth
SIG SG 552
The SIG SG 552 (called the 'Krieg 552') features an early-model ACOG scope, fast rate of fire and long, single shot range. As a result, it is used widely by those which are new to the game. The fast rate of fire allows the gun to drain the 30 round magazine in seconds with average accuracy. When firing in full auto, the range and accuracy remains average, even when using the scope. However, when using the scope and firing in semi auto, it is surprisingly accurate with a very long range. The gun is only available to the Terrorists.
Steyr AUG A1
The AUG A1 is a very powerful long range weapon similar to the Terrorist's SG 552. Called "Bullpup" in the game, its scope allows the player to zoom in close to a far way opponent and get a hit 70% of the time. Doesn't have as higher rate of fire as the SG 552, but is just as powerful, if not more. This gun is only available to Counter Terrorists. It is also worth noting that the AUG in the game is shown being chambered in 7.62 according to the HUD, vs the A1 using 5.56 in reality. The in game model is also glitched, as it shows the bolt handle not being connected to the gun when reloading.
The Steyr Scout (called "Schmidt Scout" in game) is the cheapest bolt action sniper rifle in the game which occasionally misses but, being a sniper rifle, has a very long range and very good accuracy. It has medium-high power and 10 round magazine. Pretty much useless in close quarter combat unless the player is extremely skilled in no-scoping. The in-game model appears to be that of the First-Generation Steyr Scout, distinguishable by how the scope is mounted towards the front of the rifle, rather than in the back like most sniper rifles are.
SIG SG 550 SR
Apart from a bigger magazine and less power, the SIG SG 550 SR is pretty much the same as the Terrorist's G3SG/1. Features a scope and only available to Counter Terrorists. Called Krieg 550 in the game. All SIG's are changed to Krieg, just like all HK's are changed to KM.
Accuracy International Arctic Warfare Super Magnum
Known in game as the Magnum Sniper Rifle, the Accuracy International Arctic Warfare Super Magnum is undoubtedly the most powerful weapon within the game, offering long range, near pinpoint accuracy. One shot anywhere on the opponents body will almost always lead to a kill. However, like the Scout, this gun is useless in close quarter combat.
Contrary to popular belief, the Arctic Warfare Police (AWP) is not offered in .338 Lapua or with a green receiver. The common reference to this rifle as an AWP (Arctic Warfare Police), is misguided. The biggest reason for this is due to the fact that it so closely resembles the AWP, and because the game's internal files refer to it as such. 
Heckler & Koch G3SG/1
The Terrorist's exclusive semi-auto sniper rifle is the Heckler & Koch G3SG/1. Holding 20 rounds, the medium-high power and long range is not as effective as the bolt action rifles on a large, open map. Instead, this gun should be used in small or medium sized maps, with its point-and-shoot characteristics more suited to close quarter combat.
Fabrique Nationale M249-E2 SAW
The M249 Para (actually a M249-E2 SAW with out a stock) is a 100 round defensive weapon, with a very powerful short range configuration. Its large spread over a large area leaves this gun better suited to close quarter combat. The gun is the most expensive weapon in the game, costing $5750. When shooting this gun just one round at a time, it is surprisingly accurate.
A Browning M2HB can be seen mounted on an armored vehicle in the Inferno and Piranesi maps.
M26 Frag Grenade
The M26 hand grenade is the resident fragmentation grenade in the game. However, the game calls it an HE (High Explosive) grenade, and it acts like one as well, having no shrapnel.
M18 Smoke Grenade
M18 smoke grenades can be used by the player to lay down smoke screens.
Mk 2 Hand Grenade
While the Mk 2 hand grenades are not usable, they can be seen on various Steam achievements.