Try Roatàn, an island off of the coast of Honduras. Lots of people speak english, and its abselutely beautiful, cheap food, and the lobster is abselutely wonderful (still really cheap too)...
its a kinda trecherous ride to get there tho, esp. if you dont like small planes.
2nd'd on Costa Rica, too.
also belize, maybe? i have never been there tho.