A prison guard hired to assassinate Paul Vitti uses a suppressed Beretta 92FS. Anthony Bella (Anthony LaPaglia) has a 92FS as "Nicky Caesar" on the set of Little Caesar, seen locked open when he is arguing with the armored car officers in the climax. It should be noted that no suppressed semi-automatic pistol is quiet enough to shoot in a quiet, all concrete and steel prison and have no one hear it. Even if he'd completely silenced the gunshot, the slide racking would be quite audible.
Desert Eagle Mark XIX
During Vitti's "limp sword" nightmare he tells Dr. Sobel about, Patti LoPresti (Cathy Moriarty) holds a chrome Desert Eagle Mark XIX on him.
Beretta Cheetah
Lou Rigazzi (Frank Gio) uses a suppressed Beretta Cheetah when his men bring the failed gunman into his office. Paul Vitti (Robert De Niro) also carries an unsuppressed Cheetah, drawing it from a hiding place in his trailer on the set of Little Caesar.
Glock 17
Paul Vitti (Robert De Niro) keeps a third-generation Glock 17 under his couch cushions in his trailer, which he tosses into a bag when hiding out from the police and Rigazzi's men. "Al Pacino" (William DeMeo) carries one during the planning and execution of the heist. The armored car officers also carry them in holsters.
Jelly (Joe Viterelli) carries a nickel Smith & Wesson Model 36, which he draws when a Little Caesar crew member enters Vitti's trailer. One of the Little Caesar cast members also uses one during filming.
Colt Python
Dr. Ben Sobel (Billy Crystal) asks Jelly if he can use a nickel snubnose Colt Python instead of one of the larger assault rifles. Jelly holds the gun laughing, remembering a lot of "good times" from the revolver, then hands it to him. Eddie DeVol (Raymond Franza) also carries a blued snubnose model.
Shotguns
Ithaca 37
A character on Little Caesar, the fictional TV show in the film meant to resemble The Sopranos, carries out a mob hit with an Ithaca 37. Jelly (Joe Viterelli) also has a pistol-gripped Ithaca in his armory that he offers to Dr. Sobel before the armored car heist.
Franchi SPAS-12
Jelly keeps a Franchi SPAS-12 with a solid fixed stock in his collection.
Remington 870
An armored car guard has a Remington 870, which Vitti's men promptly disarm him of.
One of the gunmen chasing Vitti and Sobel fires a Cobray M11/9 from the window of his car. Jelly also keeps one in his armory that he offers to Sobel.
Uzi
Jelly keeps an Uzi in his gun collection when showing it off to Dr. Sobel.
Heckler & Koch MP5A3
The armored car officers and fake NYPD ESU officers working for Vitti, have Heckler & Koch MP5A3 submachine guns.
UHC MP5SD Airsoft Gun
One of Vitti's men carries an "Heckler & Koch MP5SD" during the armored car heist but it is actually an UHC airsoft gun as noted by the finger groves on the handguard.
Rifles
M16A2
Jelly has an M16A2 in his collection, asking Dr. Sobel if he can handle an M16. When Sobel asks if he means to shoot it, Jelly sarcastically tells him he wants him to twirl it around his finger.
CAR-15
Jelly has two CAR-15s in his gun collection, between the M16A2 and AKS-74U. Two mobsters on Little Caesar use the CAR-15s to carry out a mob hit.