There are some newer Cryptocoins that tout anonymity using various methods of blockchain obfuscation ,of these Darkcoin has the most promise IMO as the development team has been the most transparent and have come up with several unique inovations that other coins were quick to clone.
Darkcoins unique Darksend+ blockchain obfuscation system is currently undergoing an independent code and feature review from noted Crypographer and Crypto coin expert Kristov Atlas, the results of Kristov's analysis are due in about a week
As I understand it, Darkcoin just uses
CoinJoin transactions that you can already do with Bitcoin. The
unrelated darkwallet should let you do the same thing with stock Bitcoin.
I think that
Crypotnote-based currencies show the most promise for privacy. They use "ring signatures" to obfuscate who spent specific coins. Double spending is stopped by something they call a "key image" that is somehow tied to your private key. They also split up the denominations of transactions like darksend+ apparently does.
Although the Darksend functionality of Darkcoin was originally based on coinjoin it has undergone at least 3 major rewrites since it was implemented and is now far more versatile and effective as a method of trustless blockchain obfuscation.
The main advantages over Ring sigs are the lack of any blockchain bloating ( Darkcoin blockchain = 300mb ish) and the fact that the API is unchanged from Bitcoins so merchant adoption is straightforward and proven whereas all the Cryptonote/Ring Signature based coins will require a complete API rewrite from the merchant side before they will be able to process payments.
