Supersized by Jannis Hermanns, one of the active people behind the Open Source blog software Serendipity,
offers free blogs for everyone (based on Serendipity, of course). The
idea with your own domain via a CNAME DNS entry is especially
cool.
Serendipity is a fine piece of blog software, even though I understandably prefer our own one (and it's not “only” a blog) ;)
Update: Try also our own free blog hosting service: Freeflux.net