The 'Git' version-control system is used to develop the Linux kernel, amongst other things, and it's the most powerful one I've used. (And I'm old enough to remember SCCS :-)) It takes some work to get your head around Git, but we're now using it to develop our CODA system, and it's been well worth it.

Michael came up with a nice way to number our build versions and has written it up on his blog - might be of interest if you're using Git already.

If you aren't, Randall Schwarz's talk is a good intro.