How about a good old M2 heavy machine gun firing miniature nuclear warheads for bullets? Think a UT2k3 redeemer blast in miniature. Low rate of fire (those nuclear shells create alot of heat in the barrel ), huge damage over a small area and rather limited ammunition.
Also, Id like to say that I definately would like to see U4E carry through into UT2k3, even if only in limited form. I still remember playing U4E with the original Unreal and then converting to UT, which was well timed with the purchase of my first computer with a 3d accelerator. Now that Im building my own rigs and have a rather nice AMD machine (couldnt live without my GF4Ti) Id love to see how spectacular U4E could be with the latest version of the Unreal engine.