Bob (Tracey Walter) uses a Colt M1911A1 throughout the movie on several occasions. A random goon also uses one later in the movie.
Colt New Service
Jack Napier/The Joker (Jack Nicholson) uses a Colt New Service throughout most of the film including the BANG flag gun at the film's climax. The only exception is one small edit when he pulls back the hammer in the Axis Chemical plant. A different pistol was used for this one shot.
This one appears to be a different revolver, can anyone ID it? - Diego Wolfwood Looks like a Smith and Wesson revolver of some sort to me--User: Colt Revolver Fan
Smith & Wesson Model 15-3
The Joker (Jack Nicholson) uses a Smith & Wesson Model 15-3 with a custom 21 inch barrel to shoot down the Batwing. We later see that the gun has a telescoping barrel when the Joker collapses it.
Smith & Wesson Model 19 Revolvers appear frequently throughout the film, notably in the hands of a mugger at the beginning of the film. Another Model 19 is seen carried by Lt. Eckhardt (William Hootkins).
Unknown Revolvers
There are a great many revolvers used in this movie, I will just post all revolver screens in this section, as I am no good at identifying them. Maybe someone else can.
I see Model 19s, Colt New Services, and Webleys. Maybe even more. - Gunmaster45
Hey there, decided the Batman page needed building, I'll try to split up the revolver section when I get more info, thanks for your help. - Diego Wolfwood
Webley Mk IV
Some of Joker's goons are armed with what appear to be Webley Mk IV revolvers in some scenes.
M1928 Thompson
The Joker's goons use M1928 Thompson Submachine Guns multiple times throughout the movie.
Krieghoff Model L flare pistol
The Joker uses this weapon to shoot his TV, then proceeds to hand it to Bob.
Its probably one of those WW2 Japanese double-barrel flare pistols. Or possibly a German one
Browning M1919
The guns that pop out of the Batmobile's fenders are two Browning M1919's. Seen toward the end of the movie as the Batmobile is entering the chemical plant.
GE M134 Minigun
Batman (Michael Keaton) has a GE M134 Minigun equipped on the Batwing, and uses it to shoot at The Joker near the end of the movie.