Detective David Mills (Brad Pitt) uses a customized Springfield Armory M1911-A1 with adjustable sights, mag-na-ported/bushingless bull barrel, beavertail grip safety, ring hammer, extended slide stop safety, extended slide release, light-weight 3-hole trigger, square trigger guard, and stag horn grips as his sidearm throughout the film, notabley during the climax.
Taurus PT99 AF
A blued Taurus PT99 AF with wood grips is used by John Doe (Kevin Spacey) when Detective Mills (Brad Pitt) and Detective Lt. William Somerset (Morgan Freeman) go to his apartment, and ultimately holds it on Mills before sparing his life. One of the murder victims is described as having bruises from the muzzle and front sight of Doe's pistol on their head, which seems unlikely since the barrel protrudes significantly past the muzzle, distancing the front sight from the barrel. One could argue however he cants the gun at a slight angle when he holds it on people, and in the first victims case, he had 12 hours of time to push different parts of the muzzle enough to discern it was used.