Halo 3: rocket launcher, needler
COD4: martyrdom (its not a weapon, but its so lazy and noobish that i count it anyways)
CS & CS:S : AWP or auto-snipers
i'll add more later
EDIT: oh, and its not that hard to defeat a energy sword, actually, if you've got a shotgun its really easy to dispatch from them at close distance, wait until just after he strikes, kill him, and snatch the Bulltrue... from distance you can use any medium-long ranged weapon there is (BR, sniper, etc.) and stickies (spikeys and firebombs (not in matchmaking) work too) just stick him..