If you're new to Mixits, you should check it out -- participants upload noncopyrighted samples, and at the end of the sample submission period, they're all 'released to the wild' and the Mixit begins -- your task is to create a track, using ONLY the samples provided.
You can manipulate them, put them through effects, distort them, etc. -- just make sure all your sounds are derived from the sample set...
At the end, the Mixits are made available for all to hear, download, comment on, etc.
Tons of fun, free samples, and more.