Went to Costa Rica in June a couple years back, was awesome. Went and saw a big volcano there, then swam in the hot pools. We stayed at a Hilton that was all-inclusive at the time but was converting to a spa so we got even better food than normal. Black sand beach was pretty cool too!
http://www.tripadvisor.ca/Hotel_Revi...uanacaste.html
Or another one could be Grand Cayman, stopped there on a Cruise and the G/F loved it there...Went and saw a turtle farm which was a good time. Didn't see much else but looked really nice from the drive to and from the cruise ship.