Swim with the Sharks!
It's cheap, it's fun and most of all...unique! On Ambergris Caye, hire a boat to take you to the Hol Chan Marine (any hotel will have contacts) and swim/snorkel with the baby sharks and stingray. An incredible adventure for those sea creature-lovers. :)
I loved this place. Do yourself a favor; skip Pana and come straight here. The people were friendly, the food was incredible, the accomodations good and there was plenty to do and see. There is a significant ex-pat scene, which could be viewed as a good or bad thing. Here, I enjoyed it (unlike Pana), in the form of good food, a few good movies, and interesting people to meet from around the world.
I could have stayed in this little place for a month and written a novel, if only i'd had the time (or an idea for a novel). It was clean, comfortable, and the view blew my mind. I did NOT realize there were two sides to this city until 3 days in.. this is on the Santiago Dock side, which is MUCH quieter and has the laid back ex-pat scene. There are veg restaurants and a bar showing subtitled movies.
I got fat here. I spent alot of time eating. In between meals, I went horseback riding along the base of the volcano, rented a kiyak (amazing!) and hit a secluded beach. As mentioned earlier, the bar down the path had two movies every night, and was a great place to gather.
My hotel also lived up to it's name. I woke up every morning to INCREDIBLE sunsets.