The word on the street says subversion is finally ready for prime time . You may recall some bizarre IP disputes -- apparently these have been resolved at this point. Apparently it's much like CVS, basically designed to be "a better CVS" and they've kept the CVS syntax except in areas where it really needed to be fixed. They've fixed versioning to work across file renames, directories, binary files, improved merging and branch support. Comparisons to the best commercial products come out favorably.
There's an OS X gui client as well : svnX from la chose interactive.