Beretta Cougars are the sidearms of both Officer Greg (Chris Spencer) and Officer John (Ralf Moeller). One is also used by Uwe Boll in a cameo during the Little-Germany shootout.
The Beretta 92FS is seen in the hands of of various characters, especially in the hands of Paradise police officers and the Postal Dude (Zack Ward). Near the end of the film there seems to be a continuity error where Officer Greg (Chris Spencer) steps out of a trailer with his Cougar before stepping back inside due to a hail of bullets. The next shot in the trailer shows him holding a 92FS instead.
Colt Python
A Colt Python is used by the Aggressive Panhandler (Michael Paré) to hold up the Postal Dude (Zack Ward) earlier in the film. Also a 6" version is used by a guy in the trailer park shootout. A stainless 6" Python is also used by Richard (Chris Coppola) throughout the film, most notably using it in his underground bunker and during the film's climax. One is also used by one of his goons. Interestingly enough there is a second goon that has his hands cupped to look like he's holding a handgun of some sort, though his hands are actually empty. Richard apparently didn't have enough Pythons to share.
CZ 75B
A CZ 75B is used by a man in the trailer park shootout. He appears to run empty yet he keeps aiming it and appears to mime fire it during the shootout with the slide locked back.
Glock 17
Glock 17 pistols are seen in the hands of the security guards during the social security office shootings. Also used by the disgruntled customer, who takes one from a security guard.
Smith & Wesson 5906
A Smith & Wesson 5906 is used by the Postal Dude (Zack Ward) in the trailer park shootout. One is also used by a customer at the social security office.
Para Ordnance P-14
A Para-Ordnance P-14 is seen in the hands of Faith (Jackie Tohn) during the Little Germany shootout and the trailer park shootout.
Ruger Redhawk
The Postal Dude (Zack Ward) takes a Ruger Redhawk with black plastic grips from Richard's bunker and uses it for the rest of the film.
Jericho 941 R
Jericho 941 R pistols are seen in the hands of a number of Paradise residents as they hunt for the Postal Dude (Zack Ward). Also a chromed version is used by one of the chicks in Dave's mansion during the shootout with the terrorists.
Large numbers of Mauser Kar98k rifles can be seen in Richard's (Chris Coppola) secret doomsday bunker.
Heckler & Koch G36K
Heckler & Koch G36K rifles are seen in the hands of Taliban/al-Qaeda terrorists. Some of them have their stocks removed.
AKS-74U
A AKS-74U is used by Osama Bin Laden (Larry Thomas) as his main weapon throughout the film.
Zastava M70BA2
Zastava M70BA2 rifles are seen in the hands of Taliban/al-Qaeda terrorists.
AKMS
An AKMS is seen in the hands of Taliban/al-Qaeda terrorists.
Norinco Type 56-1
Norinco Type 56-1 rifles are seen in the hands of Taliban/al-Qaeda terrorists.
M14 rifle
A M14 rifle is used by one of the Paradise residents against the Postal Dude (Zack Ward) and Faith (Jackie Tohn) during the trailer park shootout.
Shotguns
Remington 870
Used by Officer Greg (Chris Spencer) to shoot an elderly Chinese woman that didn't move her car when the traffic lights changed color.
Ithaca 37
Ithaca 37 shotguns are seen in the hands of various Paradise residents.
Mossberg 500A Field Gun
A Mossberg 500A field shotgun is seen in the hands of a Paradise resident during the trailer park shootout.
Winchester 1897 shotgun
A Winchester Model 1897 is used by The Postal Dude's irritating neighbor during the trailer park shootout. He only fires it once though.
Machine Guns
Daewoo K3
A Daewoo K3 is used by the Postal Dude (Zack Ward) for two shootouts. He manages to get out of both of the sizely shootouts unscathed and with one hundred percent casualties on his aggressors. Since Postal was filmed in Vancouver, British Columbia, Canada; the Daewoo K3 machine gun seen in this film has been used in many TV shows and movies that were filmed in Vancouver e.g. Stargate: SG1,Stargate: Atlantis, Walking Tall, Underworld: Evolution, Battlestar Galactica etc. In the trailer park scene it clearly fires blanks.
M60 machine gun
A M60 was in Richard's (Chris Coppola) secret doomsday bunker. Another M60 was used by one of the Paradise residents against the Postal Dude (Zack Ward) and Faith (Jackie Tohn) during the trailer park shootout.
PKM machine gun
A PKM machine gun is used by one of the Paradise residents against the Postal Dude (Zack Ward) and Faith (Jackie Tohn) during the trailer park shootout.
Browning M2
A Browning M2 is used by Richard (Chris Coppola) during the trailer park shootout. The M2 machine gun was mounted on a convertible car.
Other Weapons
RPG-7
A RPG-7 is in the hands of a Taliban/al-Qaeda terrorist named Abdul, a mentally handicapped terrorist. He drops it several times, the final time causing it to go off.