I'm a big fan of AOS. My girlfriend and I did our open water certification here after purchasing a Groupon. As I understand it, Groupon keeps half the money. So for about $200(after Groupon's fees) for both of us, we got all classes, materials and check dives. That's really a stellar deal considering how much time/effort it takes to certify someone. It also means that AOS probably doesn't make much money on the deal. Despite this, we were treated exceptionally well by Kevin, our classroom and open water instructor. We're looking forward to booking a scuba trip with them in the furture, and are happy to give them future business based on our past experience.
P.S. I'm a member of their virtual dive club on Facebook, all the admins are super helpful and very quick to answer any Scuba related questions.