RelMeAuth/IndieAuth seems cool. The option of authenticating with a domain + PGP key really tickles my decentralization bone. Of course DNS is not completely decentralized, but in the context of the modern web, this seems real interesting.
Also, I very much like how the user can choose whether they want to trust any specific authentication provider. Twitter's auth or your own private key, and everything in between works in a singular login system. Seems like a neat package.