Our team uses Mercurial with great success. (I also use it for all of my personal projects and our team's internal website.)
Code:
E:
mkdir robotics2011_code
cd robotics2011_code
hg init
hg clone C:/Dev/Robotics/2011/
And that flash drive is now a "server"!
Or if you aren't too keen on the command line, you can use TortoiseHg.
Another awesome feature that Mercurial has (which git does not have) is "hg serv" which is basically a minimalistic web server that hosts and interface to your mercurial repo.
I can also say I've been happy with git, but it sometimes acts funny on Windows. It also likes to slow down after time if you don't manually garbage collect frequently.