Martin Fowler has recently posted an article about the Subversion revision control system on his blog. The best line:
On the basis of my informal conversations with my colleagues, Subversion (abbreviated to SVN) is a better system than all the commercial tools except Perforce.
Subversion is an open-source replacement for CVS. It claims to solve the major problems of CVS--namely, lack of file renaming, no revision control of directories, and performance that's linear to the number of files in the repository. (Instead, Subversion claims performance that's linear to actual bytes changed, which in practice would be a huge, huge speed-up.)
I've been looking at Subversion with interest for years, but was waiting to see it in more widespread use before recommending it to my customers. It looks like that day may be here.