the redeemer from the original UT was the best. All you have to do is camp the back of the base in facing worlds and you can fly that thing around FOREVER.
Until it/you explodes.
the SUPER shotgun from doom FTW
from ut'04 that ion cannon laser painter thing. THAT was cool.
proximity mines from Goldeneye.
Anti-personnel weapoin from Red-Faction
so many good ones