I am currently not using any form of version control, although I would really like to get in the habit of using one. From what I have read there are really 2 good options, SVN (http://subversion.tigris.org/) and CVS (http://www.nongnu.org/cvs/).
You can also subscribe or get spaces on the internet that supply loads of tools in addition to version control. These places are ideal multiple people to collaborate over the internet and still have access to the same files and communicate efficiently. Assembla (http://www.assembla.com/) is one I have used in the past and it works pretty well. The one drawback is it used to be free, not sure it still is for private spaces.
