These sites are dedicated to video game re-arranging.

Dwelling of  Duels - Monthly competitions with video game arrangements featuring live instruments.

Metroid Metal - Metroid! Stemage does some really tight metal interpretations...if you're into metal you must give this a listen.  And if you're not, it just might make a believer out of you...

Big Lion Music - Jake Kaufman, the guy behind vgmix and some great music.

Ryan8bit - Ryan8bit has baked some tasty guitar remixes.  He also has a full Castlevania 1 and 2 album.  Don't miss his "Punching Dogs" remix!

Minibosses - The minibosses tour and play video game music, and have a great community.

Overclocked Remix - This site introduced me to game arranging.

OneUp Studios / TheOneUps - They make official remix albums...check it out!

Fallen Heroes:

VGMIX - A great game-arrangement community.

Ailsean's Game Remixes - Sean Stone, aka "Ailsean," has some extremely polished stuff here.