The following weapons were seen in the film National Treasure:
The Glock 17 is carried by several FBI agents and are also seen in the holsters of the Philadelphia police. Shippen (Oleg Taktarov), one of the henchmen of Ian (Sean Bean), is also seen firing a suppressed Glock at the van of Benjamin Gates (Nicolas Cage) before the chase.
Jericho 941 R
The Jericho 941 R is seen several times during the film. It is first seen when Shaw (David Dayan Fisher) pulls a stainless Jericho on Benjamin Gates (Nicolas Cage) inside the Charlotte. Shaw then uses it suppressed during the break-in at the National Archives and the chase through Philadelphia. Other Jericho's are seen in Ian's catering van.
Note that in the picture you see Shaw's stainless Jericho being loaded, you can see a shotgun in the background.
Heckler & Koch MP5A2
A Mossberg 500 is seen among the equipment Ian and his crew prepare before attempting to steal the Declaration. Many FBI agents at the end of the film can also be seen with these shotguns as Ian is arrested.
One of Ian's Henchmen uses a Advanced Taser M26 on one of the security guards during the break in at the National Archives.