Originally Posted by Take Your Lumps
It's a little bit of a trek, but I highly recommend going out to Culebra island and checking out Flamenco Beach.
One of the most amazing beaches you will ever see.
You can take a cheap ferry boat from Fajardo or if you have the dough to spare, you can catch a small charter plane from San Juan.
Culebra is definitely nice, though I suggest spending a night out there at one of the resorts. It takes awhile to get there from SJ and the ferry stops running @ 4-5 I think and the last flight is just a little after that.