rocket submachine gun from that quake 2 enhance weapons multiplayer mod. a machine gun that fire rockets, wow.
There was also a UT 2004 mod like that called the OMFG Rocket Launcher.
More great Unreal/Unreal Tournament weapons:
Biorifle (aka "goo gun") -- shoot little gobs or hold the secondary fire button and release it to shoot out a large goo goober.
Razorjack/Ripper -- fires spinning razor blades that can ping off of walls.
Flak Cannon -- fires red hot pieces of flak that can bounce off walls
Shock Rifle Combo attack -- the secondary fire shoots out a ball of plasma and if you hit with a primary fire laser bolt you get an area-of-effect explosion. (This was the weapon and attack of choice of the clanner pros.)
8-Ball/Rocket Launcher--loads 6 at a time and then fires them off.