I would say that svn is more than adequate for most projects (CB uses it). some of the distributed version control systems may work better for larger groups: add bazaar, mercurial and git to your list. I have personally use bzr on my local network and usually svn for hosted projects. all of these are free + open source software
the ones I mentioned are command line tools, but it wouldn't be a stretch to integrate some interfaces for them into CB (for example, I created a simple file browser that shows the status of files checked out from bazaar, mercurial and svn repositories in my ShellExtensions plugin -- you can check it out by following the link in my sig)