This morning I was reading this post, and I must admit that even I with my AbstractView project use Subversion (Google Code) to keep track of the sources of the project. Team Foundation Server and the features exposed through codeplex are really amazing, but when it is time to speak about Source Control I think that Subversion is a product really superior.
I use Subversion not only with Google Code but also with a dedicated server to keep all the source code of the company where I work. Subversion has great performance, it has high integration with the shell (Thanks to Tortoise), has really a lot of options. To be operative with subversion you have to download a little more than 10 mb opposed to 140 mb or more that you needs to download to integrate with codeplex.
In my opinion Subversion is probably the most interesting source control system, and it’s freeware :D