The "symptom checker" tool over at Web MD is pretty cool. The advantage here is that you can just start with your symptoms and it guides you through a little diagnostic routine and presents some possiblities...on the other hand, I see way too much self-diagnosing going on so I'd also like to see a major disclaimers as to the limitations of such a tool.

By the way, I think the "buddy list" idea is worthwhile. Not just as a replacement for the Who's Online feature here, but I think it stands on its own as a cool idea for an ideal mental health website.