ATF Agent Derrick Vann (Samuel L. Jackson) carries a Smith & Wesson 5906. In the scene where Andy Fiddler (Eugene Levy) is being interrogated, the Internal Affairs agent claims that a ".45 slug" is the same as Vann's gun, but the barrel is too small to be a .45.
Walther P99
Andy Fiddler (Eugene Levy) accidentally pulls out a Walther P99 with a stainless steel slide from the bag delivered by Joey Trent/Kane.
An ATF agent also is seen crashing through a skylight armed with a Heckler & Koch UMP.
Colt AR15
Seen being stolen from the police station, might have also been M4A1s though, as Derrick is being briefed at the beggining of the film on the stolen weapons.
Jennings Model 38
Street hustler Booty (Anthony Mackie) is seen selling what appears to be Jennings Model 38 pistol to a plus-sized street girl, he describes it as a "nickel plated ladysmith nine mary-mary". According to that dialogue, "nine mary-mary" is slang for 9mm.