I just booked a flight to Miami for 2 weeks at the end of Jan 2011. We will be flying and staying in Grand Cayman for a few days during that period but for the rest of the time,we are hoping to hire a car and were looking for suggestions about places to visit in the area for a few days. e.g. Florida Keys, etc

Any suggestions about places to visit and stay? Also, as it is probably a busy period would it be okay to just turn up at a place and get a room? or would it be better to book these places in advance? Are they cheaper then?