Cayman islands and Bonaire are the common answers to this question but Bahamas, Belize, Cozumel, Saba, Bay islands, and others deserve a mention too.
Read more: http://thorntree.lonelyplanet.com/messagepost.cfm?postaction=reply&catid=50&threadid=1303449&messid=11381462&STARTPAGE=1&parentid=0&from=1 .
