The Keys are my favorite part of Fla. In addition to No Name on BPK. I'd also suggest going to Fish Cutters on Summerland Key- get the BLT (Bacon Lobster and Tomato sandwich) My mouth is watering just thinking about it. There also are a number of great Tiki Bars throughout the keys. If you go to Key West, I would recomend a lot of that aren't on Duval Street (Schooner Warf Bar- Try to catch a Michael McCloud performance while you are there, he is very Jimmy Buffett- esque). The Mel Fischer Museam is also cool (lots of wreck treasures). On a more touristy note- sunset at Mallory Square and a photo op at Southern most point are not to be missed. I havent' been there yet, but I know my parents really enjoyed the Dolphin Research Center when they came to visit me last year.
Miami- South Beach is a must- lots to see there- Lots of 50s Art Deco Hotels (don't miss the Deleno), Lots of latin Flair- Mangos (a salsa and merenge night club) is definatly up there on the list. One word of note in Miami- is be careful not to get lost- there are some REAL BAD parts of Miami too.
Enjoy your trip!