Darkcoin is apparently- if you believe the chatter- the truly anonymous, successor to Bitcoin. May the Bestcoin win...

The money quote (pun only partially intended):

'Darkcoin adds an extra layer of privacy by automatically combining any transaction its users make with those of two other users–a feature it calls Darksend–so that anyone analyzing the blockchain has a harder time figuring out where a particular user’s money ended up' - via Wired's Andy Greenburg