I second Puerto Rico only because of my bias and the following reasons:
Hot girls
drinking age is 18
no currency exchange - US dollar
they speak English and Spanish
tropical weather
http://www.gotopuertorico.com/
Isla Verde in San Juan is the touristy attraction and where you should look for hotels. Since I have family there, I just stay with them. Another place in PR you should look at is Vieques. It's an island off Puerto Rico that is part of Puerto Rico. It's where the Navy used to do their practice drills. Navy no longer occupies the island and the government has cleaned it up. Since then it is now home to one of the most beautiful beaches in the world.
http://www.gotopuertorico.com/puerto...es-culebra.php