I’ve heard nothing but excellent reviews from visitors to Thatch Caye Resort (tel. 800/435-3145, www.thatchcayebelize.com [1]), an island complex nine miles from Dangriga [2], within the South Water Marine Reserve.
The “handmade eco-resort” consists of four casitas and seven cabanas (with en suite bathrooms, king beds, ceiling fans, and plenty of lounging room), which were constructed without the use of heavy equipment. They’re run by solar and wind. There’s also a family villa and a soaring thatch-roof dining palapa.
Various all-inclusive snorkeling packages requires a three-night minimum stay (US$611–775); that means all meals, three guided snorkeling trips, unlimited use of sea kayaks, and round-trip water transfer from Dangriga.
Camping is allowed on the island for US$15 per person; you must have your own equipment and are welcome to join other guests in the dining room for meals.
Links:
[1] http://www.thatchcayebelize.com
[2] http://www.moon.com/destinations/belize/the-southern-coast/dangriga