Darcs is yet another one -- http://darcs.net/DarcsWiki
I've just started playing with it for personal projects. CVS is too crufy, and Subversion has too many requirements for my personal stuff (though we moved from VSS to Subversion at the office and have never been happier).
Back to darcs -- the commands are easy. It seems to be distribuated when you want it to be and centralized when you want. The fact that you can immediately mail patches back and forth, and pull any source tree off the web and into are cool features.