Best source control development tool for Windows / .NET

You can use TortoiseSVN and any Visual Studio plugin for svn: AnkhSVN or VisualSVN.

EDIT:

Quite some time has passed. If I were to answer this question today, I'd strongly recommend using git. I personally use it even when working alone. I didn't try to integrate it into Visual Studio, but standalone app SourceTree serves me well. If you never used git before I'd recommend reading Pro Git book (it's free). Evening or two spent on it will pay off.

Team Foundation Server is probably the most integrated into Visual Studio.

However, I personally love Kiln (which also integrates nicely into VS). This is nice for a small team, being hosted and very elegant and easy to use.

Other options include Subversion and Git. However, without knowing more requirements, it's difficult to suggest the "best" option for a small .NET team. Self-hosted vs. hosted for you is probably the largest factor in making your decision...

Take a look at Perforce. Free version allows something like 2-users, 5 workstation. Paid version is reasonable as far as configuration management tools go.