I had good results with Bovada a few months ago when I played there, decent site and legit from all the threads about them that I've read on Reddit and elsewhere. Also available to Americans the last time I checked if that applies to you.

There's some negative feedback on the Bitcointalk account representing NitrogenSports at the moment (click for link), and as far as I can tell most of the issues raised by the negative feedbacks have never really been fixed, so I can't recommend the site at this time. Used to be decent back when I did use the site though.