The weapons of Far Cry 2, especially that bolt action sniper rifle - M1903 iirc, and the AK. This game might be a bit shallow, but it has nice guns.
RMQ super shotgun, especially Demo2 version.
Quake lightning gun.
Doom 3 pistol, after I upped the damage via script.
Red 9 in RE4.
Hunter rifle in Prey, zoomed.
The weapons of Crysis (1), especially pistol, AK74 and SCAR, although they feel very "tight" / "hi-tech" to me and I now prefer a looser / oldschool vibe.