There has been a fair amount of buzz lately about Basecamp. Basecamp is basically an online project management tool and client extranet. It actually looks like a pretty good system. You can track all communications, client reviews, milestones, and tasks. It also allows you to easily share files.
Basecamp is sold as a monthly subscription, not a one time purchase fee, because they are hosting the entire thing. I personally would like the option to buy the system and host it myself.
I personally don’t find a huge need for it (for myself), but that is only due to the scale of my projects. I typically only coordinate with one person per project. But, if you’ve been looking for this kind of tool, Basecamp could be the answer.