The ability to report posts/debates. Currently we can report a comment or report a user; but we can't report a debate.
A reference section on critical thinking and logical errors (I'd be happy to help write that myself).
Buttons for declaring "concede" and "fallacy".
Super-users with very limited administration rights (e.g. can delete a reported comment/debate; but cannot ban users and with no access to IP address information).
Someone else said that and I agree, the ability to make polls without any actual debate.
Guest debaters. We set the debate topic and invite guest debaters who are knowledgeable in the topic to debate the issue.