Git is the new hotness.  There are other distributed version control systems, but git seems to be the one that’s taken off the most from what I’ve seen.  There’s Mercurial (the command “hg” is pretty sweet) or Bazaar (does anyone use this?), but it seems that most all of the projects I’m interested in that use dvcs are using git (I’m looking at you IronRuby.)

Git may be a bit confusing when you first start working with it, but fortunately, http://gitready.com/ has a bunch of tips for dealing with git day to day.