https://www.torproject.org/docs/tor-hidden-service.html.en

There are other projects, like I2P and Freenet, but they aren't as widely used and they are slower.

There are tons of hidden services in Tor:

http://en.wikipedia.org/wiki/.onion

EDIT: There's also namecoin, that someone submitted:

http://news.ycombinator.com/item?id=2546815

EDIT2: And the MafiaaRedirector Firefox extension:

https://addons.mozilla.org/en-US/firefox/addon/mafiaafire-re...