The snorkeling in Belize, even in the more visited areas around Ambergris Caye, is superior to almost any other snorkeling in the Caribbean. You do have to take a boat out to enjoy the best snorkeling -- and no, boats are not available for rent -- but that's not such a hassle as you might think. You can make a fun trip out of it, and contrary to what you might think, you'll get more snorkeling in than you probably want to do. In between trips, you can snorkel off the shore, around docks, etc.
There are many different small condotels and suites places along the beach south of town, starting with The Palms and Belizean Reef Suites just south of town, and among others Caribbean Villas (litle "mini reef" around the pier), Woody's, Coral Caye. Near Banyon Bay is Banana Beach, which has lovely one-bedroom suites.
Belize First Magazine http://www.turq.com/belizefirst/