We stayed at Ramons Village,
http://www.ramons.com/ , on Ambergris Caye, in Belize for our honeymoon back in May of 2006. We had our own cabana, steps from the water. There is a lot of mixed reviews (
http://www.tripadvisor.com/ ) with this resort, but we had a fantastic time. One thing to keep in mind is you are in a third world country, and most of the hotels and places to stay will reflect that. It is one of the more expensive places to stay on the island, and the food is expensive and not very good, but it is within walking distance from town, which has a lot of cheap and good places to eat.
We dove for 5 straight days with their onsite dive shop. The final day we were able to "bribe" the dive master to take us on one final dive that we would remember, and he took us to some tubes/caves, and it was truely a dive that my wife and I will always remember. We were within arms reach of sharks on every dive and were able to see eels, rays and turtles on almost every dive.
If we were to go back, I would dive with Ramons again, but I think we would find a more reasonable place to stay.
Hope this helps.