If you are on the look out for .com domains or for usual domain extensions, you get them from Squarebrothers.com. I find it cheaper and I suggest it because, I've been purchasing and using squarebrothers for more than two years and I experienced no trouble with them.
(But don't choose for hosting with squarebrother servers)
You can't find all sort of domain extensions with them. So if you looking for special extensions(.xxx, .am, .me) etc.. you can get 'em from GoDaddy.com