Remix Fight!

Here's a fun place for remix contests: Remix Fight!: "Remix Fight! is a remixing community open to everyone. We get people to send us source files for their songs and then make that source available for download. People download that source, make a remix, and then e-mail an mp3 of their mix to us. Then, we post all the mp3s we’ve received and set up a poll so that visitors to the site can listen to the mixes and vote on which one they like the best. After a couple weeks, we close the poll and announce a winner."

Fourstones, who is the mastermind behind ccMixter.org has often said, that Remix Fight has been his inspiration for ccMixter.

Songpull

Here's a nice concept for songwriters suffering from difficulties with finishing a song: Songpulls offer songwriters a place to gather and try new songs in an encouraging environment. Inspired by the classic 'guitar pull' of the past, the Songpull community gives genuine feedback and recognition on every performance. Finish your songs by joining a Songpull today".