Use a distributed version control system. There are many out there the most popular ones being git and mercurial. Distributed SCM is really the way to go because they tend to have much better branch merging and branch management algorithms. Also, by their very nature they are stand-alone programs processing your filesystem. So you don't need to install or manage a server which is another plus for a personal version control system.
Like Tyler, I would personally encourage you to learn git (because all the cool boys use it :-) but I know it is not for everybody. If you like GUI Plastic SCM looks very good. It's commercial but free for teams of less than 5 people. Fossil is another one that's easy to use (I would say easier than git to learn) but it uses an SQLite file to store your code and I'm not sure if it scales to really big projects. On the other hand SQLite itself is a fairly big project that uses Fossil (both written by the same author for the same reason: he couldn't find anything else out there that he liked).
