Have you heard about CodePlex?
If you are familiar with SourceForge, you might want to check out CodePlex. According to their website, CodePlex (www.codeplex.com) is "Microsoft's open source project hosting web site." It has a lot of the features that SourceForge provides (issue tracker, discussions, source code distribution, etc.), but has one really cool feature: it is based on Microsoft's Vistual Studio Team Foundation Server. This means that it can be tightly integrated into your Visual Studio development environment.
I'm no developer, but CodePlex seems like a really cool idea. In fact, a number of Microsoft project teams are actually participating in community development efforts using CodePlex. Check it out at www.CodePlex.com.