How do I set up filter for certain registrable email addresses, any ideas?

I think you mean an exclusive whitelist, other domains than on it can't be registered?! I also thought about such a function many many times. Most of my community members just use the biggest public email providers (f.e. gmail.com, aol.com etc.), there are only very few others (most of them is spam or temporary junk email addresses) and I could imagine it would be worth for real users generating one of these allowed public big player email addresses if the registration domains are limited. It would save us a lot work with blacklisting hundreds of domains every month again and again.

Or at least a function, "IF not whitelisted THEN requires admin validation)

+1 Any ideas?