Agree on the SCUBA, it's sooooooo much better. But if you're really into snorkeling, San Salvador offered some good stuff when I was there. The island is pretty off the beaten path so to speak, but good snorkeling. Although I've never been there, I'm told you can snorkel lots of the GBR, but then again, if I was travelling halfway across the world, I'd want to be SCUBA certed for that. Also just got back from a trip to Maui and there was really fantastic snorkeling there. Ahihi nature preserve was probably the best snorkeling. Molokini was much better for diving than snorkeling, although the vis is truly spectacular there.
Don't forget, a lot of dive shops will do "referral" courses. You take the classes and pool times for SCUBA here in WNY, but do your cert dives at nice tropical places. One of the boats I took in Maui had just some folks on it.