Subversion is a useful version control system, designed to fix all the problem that CVS have.
- Tortis SVN: Hooks into your windows file system directly and supports patch.
- Smart SVN: Came in as recommended to me. I think the advantage is that you can shut it down any time you want.
- SvnKit: Formerly known as JavaSvn. The one that pretty much all the IDE SVN integration uses.