I think mine would be:
Assassin's Creed: one archer on top of a tower in the Kingdom was standing kinda diagonally. It even fought in that position, and it happened all the time I approached it. Anyone else had it?
Land of the Dead: Road to Fiddler's Green: zombies would start to attack, but instead they would scream in one place. If you went far away from them they would go on with their zombie business but when you approached them again they would do the same screaming for eternity thing.
Big Rigs Over The Road Racing: Ha. Ha. This whole game is a fucking glitch. And yeah, I've bought it, even if it was 1000 Forints (about 5 bucks).
Still Life 2: Vic would sort of "collapse" at one point and the game couldnt go on. Was weird, looked like if the character model had a seizure and gave up playing...
Jedi Outcast: not a glitch, but I spawned a lot of stormtroopers into the last room where you fight the final boss, then noclipped back to an earlier place and walked into the room. A cutscene was triggered and as Kyle walked in and started talking all the stormtroopers would shoot him to pieces. Funniest thing: he and Desann would continue to converse, even though he was already dead.
Hitman: Blood Money: God this is a goldmine of funny stuff. Once the sheik you have to kill in the casino was freaked out by me when I was running around in the room, and then ran out. Now, if you leave that room, all the guards are going to shoot you. Then, when thinking about what I should do he was teleported back into the room and got the phonecall, according to the gamescript, and then proceeded to leave the room, but in the wrong direction. What more, he went right through a fucking wall. I was laughing my ass off. Then there was a guard who I strangled near that waterfall in the second level, after which he appeared on the thin air walking out in nothingness towards the waterfall. Then he took a slow turn, looked at me, readied his gun (as if he just recognized me) and finally started falling down. Looked like a Looney Tunes cartoon with a twist. But my favourite is the part when I threw off a worker from the railing above the stage in the opera house in Paris, only to have all the guards run towards him and tell the corpse to get off stage... This game is only made more awesome by its enormous bugs.
And lastly, not mine but had me laughing on the floor:
http://www.youtube.com/watch?v=6tZoqpKFMzA