Better not do it, it's not very user friendly. Most people want to use free accounts to prevent spam from sites they don't trust. We just keep ip banning untill they are tired of it. You could give your moderators ip banning functionality ...
Who has a updated list? And how do you go about doing it? add *yahoo.com in the banning area right?
There are too many sites to possibly list offering free e-mail accounts or disposable ones. Seriously, a list would be like 10 pages plus long. Oh, and don't forget the address of anyone's site using a certain modification here.