There's http://www.mathoverflow.net http://www.mathoverflow.net -- I can't vouch for whether it's good or not, as my math sucks, but it seems like it might be u

There's http://www.mathoverflow.net http://www.mathoverflow.net -- I can't vouch for whether it's good or not, as my math sucks, but it seems like it might be useful and I stumbled across it on a usually reliable site.