What time of year are you going? Where are you traveling from? What is your budget?

Depending on time of year, you might want to look at the Out Islands of the Bahamas -- though they can be difficult to reach, and chilly in the winter. Aside from those concerns, you get quirky but comfortable lodgings, spectacular beaches, and a laid-back feeling that isn't matched anywhere in the West Indies. Your travel style, experience (especially with small boats) and budget might dictate one island (or island group) over another, but take a look at the Abacos, Exumas, Eleuthera, Long Island, Cat Island, Andros, etc.

There's lots to see and do in Belize. Many people split their time between one of the jungle lodges around San Igancio and one of the beach destinations.

There's also the Toledo district in southern Belize that has some interesting sounding activities, but, I haven't been (yet). Not nearly as many tourists there.

Around San Ignacio, there are several Mayan sites, several caves to explore, cave tubing, zip lines, hiking, canoeing, horseback riding.

Off the coast is the barrier reef, world class diving and snorkeling. Good fishing, including flats fishing. Several funky beach towns.

Belize is small and easy to get around. Going from place to place won't cost you a day of travel time.

http://www.travelbelize.org/