The following firearms are seen in the film Donnie Brasco:
Two of the Mafioso, Dominick "Sonny Black" Napolitano (Michael Madsen) and Nicky Santora (Bruno Kirby) use Beretta 92FS pistols. Nicky's is clearly seen when he executes Sonny Red (Robert Miano) with a shot to the head. (The 92FS is an anachronism, as the film takes place between 1978 and 1981, before the 92FS was introduced). It would have been more accurate to use a Beretta 92 as they were introduced in 1976.
Benjamin "Lefty" Ruggiero (Al Pacino) finds a M1911A1 with ornate grips hidden in the basement where Sonny Red and his cronies were killed. Mistakenly referred to as ".9 mm" by one of Sonny Reds men.(.22 revolvers can be seen behind he 1911s)
Benjamin "Lefty" Ruggiero (Al Pacino) uses a Beretta M1934 to execute Nicky (Bruno Kirby), not a S&W Model 39 as previously mentioned. Note: This could also be a Beretta M1935 if you can tell which one appears in the film please specify.
Smith & Wesson 39
Paulie (James Russo) uses a Smith & Wesson Model 39 during the killing of Sonny Red. Benjamin "Lefty" Ruggiero (Al Pacino) also uses a Smith & Wesson 39 to intimidate Donnie (Johnny Depp) into killing Sonny Red's son.
Smith & Wesson Model 36
Benjamin "Lefty" Ruggiero (Al Pacino) carries a Smith & Wesson Model 36 revolver when he asks Donnie Brasco (Johnny Depp) about the yacht they used while in Miami. He then gives the gun to Donnie to use to kill Sonny Red's son.
FBI agent Joseph Pistone (Johnny Depp) is seen on the firing range with a "Pre-B" CZ 75 at the end of the film. This scene was only added because the studio wanted a shot of Depp firing a gun to use in the trailers.