We have been using Visual Source Safe 2005 (using SCC Switcher plugin) so that it works over internet.
I heard that VSS has issues when project size is large numbers of users more. But with our team of 7 programmers for one not-very-large project, we faced many issues, like files getting corrupted, missed check ins, and file management issues.
So i decided to go back to good old SourceJammer. Its free and the best option if you dont want to spend money and dont want advanced features like Branch promotions etc.
Here it is: www.sourcejammer.org