subversion (http://subversion.tigris.org/) has been gaining lots of momentum lately, and I just saw this link today:Oh, & CVS is free which is always a good thing. :)
http://svnbook.red-bean.com/
some of you might know the folks at red-bean from their other projects, like http://cvsbook.red-bean.com/ and cvs2cl.pl (http://www.red-bean.com/~kfogel/cvs2cl.shtml)
HTH
--Geoff
