So I'd be grateful if someone could compile a list of significant contributions made here that would be useful to professional philosophers, with links to sources.

Actually in one case this "forum" could benefit from the help of professional philosophers, as the founder Eliezer Yudkowsky especially asks for help on this problem:

I don't feel I have a satisfactory resolution as yet, so I'm throwing it open to any analytic philosophers...

I think that if you show that professional philosophy can dissolve that problem then people here would be impressed.