http://anonymixrscb7ytw2sau6kqyn2tocg4dooz3bdlanetakgvwcch2i5yd.onion/en/index.html
Here's how it works: You send us bitcoin, and we send back new bitcoins to a new address that you control. This breaks any continuity on the blockchain between your old activity and your new coins, making it nearly impossible to follow the new trail. For extra anonymity, you can choose to delay your mixer payment, and send your new coins to more than one address.