Subversion is the defacto open source source version control system these days and a great improvement over cvs. It’s also a steal at the ripe price of free.
Great (and also free) documentation is available here: Version Control with Subversion.
You can also buy the hardcopy from Amazon.
To use any subversion repository you will need to install the client. For OS X, I wouldn’t recommend using Fink but rather downloading a pre-compiled binary, they are more up to date. Binaries for OS X are available here: www.open.collab.net/downloads/subversion/
For eclipse, there’s a handy plugin called Subclipse.
For small projects or distributed development teams not looking to manage their own subversion server: unfuddle.com has a great hosted solution and an integrated milestone and ticketing system.