Pistols
PM Makarov (PMm)
PB6P9 (PB1S)
Fort 12
Walther P99 (Walker P9M)
Desert Eagle (Black Kite)
H&K USP (Compact UPD)
Colt M1911 (Kora 919)
SIG Sauer P221 (SIP-t M200)
Some weird huge Russian pistol that is fitted to use rifle bullets, 9x39mm. Couldn't find the name. (Big Ben)
Supposedly there's also a Browning Hi-power and a Beretta 92FS in the game, but I haven't found them.

Rifles and SMGs
AKS-74U (Akm-74/2U). Special version with a silencer in game.
AKS-74 (Akm-74/2). Special version with an increased firing rate. Can be fitted with a PSO-1 scope and a GP-25 grenade launcher.
OC-14 Groza (Tunder S-14). Has an "integral" GP-25 grenade launcher. Cannot be mounted with scopes, but that's probably a bug.
LR-300 (TRs-301). Can be mounted with a SUSAT scope and M203.
G-36K (GP-37)
AN-94 Akaban (Obokan). Special version with GP-25. Can be mounted with a PSO-1 scope.
L-85A1 (Lightened IL-86)
MP-5A3 (Viper 5). Special version with a silencer (called a "Noiseless Viper", probably a MP-5SD3).
AS-VAL (VLA Special Assault Rifle)
SIG 551 (SGI 5k). Special version with a SUSAT scope.
There also seems to be a FN-2000 somewhere in the game.

Shotguns
It looks like a shortened version of a Winchester 1300. In game it is called Chaser 13, so this might be right.
TOZ-34 (Haven't found it yet, can't tell in game name)
SPAS-12 (Haven't found it yet, can't tell in game name)
Some random shotgun called "Dbl barrel sawn off". It's exactly what it says it is. A sawn off double barrel shotgun.

Sniper rifles
SVD (SVDmk2)
SVU (SVUmk2)
VSS Vintorez (Vintar special sniper rifle)
"Gauss Rifle".. Who knows what this could represent? It looks weird. It's like a railgun.

Heavy weapons
RPG-7 launcher (RPG-7u)
RG-6 / 6G30 (Bulldog-6)