Post links to your favourite ones here. If you've got links to other places, like boredatwork.com or something, go ahead and throw them in, too.
Counter Struck
Probably more entertaining for nerds who've played the game, but it's possible to appreciate it for the technical aspects even if you're not a big CounterStrike player.
CounterStrike: Vents
Be warned of severe profanity(Various F-words, threats of rape, etc.), most likely to be hilarious if you're a bastard at heart. Basically it's a bit of minor "griefing" to which some poor 15-year-old overreacts completely.
George Washington rap
Some profanity, talk of testicles, sex, etc. not hideously offensive unless you're overly touchy, but utterly hilarious either way.