El Yunque is awesome - definitely gotta make your way there, but make sure you go at the right time. If you go too late in the day it's raining too much and lots of areas get closed off due to mudslide risks.
Old San Juan is kind of a given. That's probably where you'll be flying in to anyway. I didn't get a chance to check out the city as much as I would have liked but it is a really neat looking place. Traffic is nuts and it cat be hotter than hell, but definitely stroll around and check it out. I think the huge farmer's market place in there as well - which is a great place to see. Lots of exotic produce and interesting faces roaming around. Well, the faces roam... not the produce O_o
I was supposed to travel by ferry to the Gilligan Isles but for some reason the boat wasn't going there on the day I was supposed to go. We took a ferry to another place instead and it was beautiful! I wish I could remember the name of the island though... either way I'm sure that any island you decide to take a ferry to is going to be gorgeous.
One of the places I wasn't too keen on was Ponce. Someone kept telling me that it's a very photo friendly place but it just didn't do it for me - probably because the stifling heat (this is coming from a native texan mind you) was almost unbearable. Also keep in mind that I was there in December! The place is just really sort of dusty and heavy feeling, so the heat seems worse there than in other places. The architecture is quite pretty though - a Spanish Colonial type square with a lovely little fountain. If you're in the area it's probably worth seeing.
These are my photos from
PR, if any locations stand out just ask and I'll try to find out exactly where they were:
http://bagofbees.pocketmole.com/Puer...uertorico.html