I just graduated. I don't think you're going to hurt anyone's feelings if you accept any email address and let folks specify their school. This is a great idea though and I hope it gets use.

Allow any email address.

I'm at mcmaster, which has a mcmaster.ca address. I don't think it's possible to match on email address to allow all schools, so just ask for the school that someone attends. If you let some non-students through, what does it matter?

Matching *.ac.?? will enable a lot of European schools and universities. Not all cctlds have the .ac second-level domain though. Some countries have 3-letter second-level domains, so I have no idea whether .edu.[CC] exists anywhere.

Unfortunately, not all countries have a standard TLD for schools. I think the only way around it is with a whitelist of domains, but I'm not sure where the list would come from. Maybe someone has created it already? Either that, or use the facebook API.