Cleanbit is a mixing service which launched in May of 2012. Their laundering procedure uses clusters of wallets to mix coins. The have optional PGP encryption available for each transaction to hide the incoming/outgoing addresses of a mixing transaction. They are the first mixing service which guarantees customers will not receive their own coins back.
They recommend using bitcoin coupled with a socks proxy or TOR when mixing to maximize anonymity.
Caution: This service is operating anonymously. Use at your own discretion.