I have been developing a bitcoin mixer service for the last 6 months, it took time because of the security and features needed for a bitcoin mixer to break the link between your bitcoins and to not be possible to detect a mixer was used.

The main features to prevent blockchain analysis are
1. No taint to original coins
2. Randomized fee (1.9% to 2.1%)
3. Randomized delay (optional)
4. Multiple destination addresses (optional)

For your safety there is a downloadable "Anonymizer Guarantee" (signed pgp message) to prove that the Anonymizer address was generated by me and that the destination addresses received from you are the correct ones. For everyones safety the site is also only available via Tor, the address is anonymizer5lg2fz.onion