I think the top three I've seen for collaborative development (whole projects) are these:
GotDotNet Workspaces - seems okay, but some folks are mentioning source control and other problems
SourceForge - lots of good stuff, nice web browsable cvs interface. lots of it is GPL'd, which can be - well, let's just say “a complication“.
VaultPub - NKOTB?
I'm interested in feature comparisons, user experiences, etc. Thoughts?