DOMINICA!! An un-touristy island paradise! I loved it! Good eco-touristy things you can do; lots of hiking, snorkeling, scuba, hot springs, waterfalls... but it a 3rd world country with some sad living conditions for the locals. But the Dominicans are incredibly kind people who open their hearts to you as soon as you arrive!
Here, I wrote up a thread about the island earlier this year: http://bestdestinationwedding.com/forum/t8253