http://www.ocremix.org/

Basically, this is a site where users submit remixed video game music. There's some awesome stuff amidst all the not-so-awesome stuff. Not too sure if any other site has the exact same stuff, but this is the one I use the most. To put it simply, it rocks multiple pairs of socks. I think I've already mentioned this once or twice before and even posted some links to songs. If you haven't already seen it, go check it out NAO.

Some OCRemixes I especially like (and will hopefully make a good first impression on you):

Dr. Mario 'Burning Up'
Tetris 'GiftFromMoscow'
Tetris 'Piano Concerto in A Minor'
Tetris 'Thirty-Plus Mix'
Tetris Attack 'Final Panic' (um, the actual remix sounds better than its name, trust me)
Bubble Bobble 'This is Not a True Ending (Asphyxiation)
Chrono Trigger 'Subterranean Opus'
New Super Mario Bros. 'Mushroom Maddness'
Super Mario Bros. 'Bowser is Pissed'
Mega Man 'Cutman Sonata'
Super Mario Bros. 3 'aquacadence'

A dozen (okay, eleven, I wasn't paying attention) diamonds in the proverbial rough, and that's only barely scratching the surface. No Advance Wars or Pokemon remixes sadly, but still pwnsome stuff there.

And on a side note, anyone know what program the people there use to make the remixes?