As you know, just about every western Caribbean cruise stops at Jamaica and Grand Cayman. Many go to Belize too, which is still very much a rustic place. But they are trying hard and there are some good tours there.
We did a great western Caribbean during New Years of 2004/2005. This was an 8-day on the Carnival Legend which went to Costa Rica and Panama, as well as Belize. I'm not sure if they still offer this itinerary, which was quite interesting and something different.