Hiya
We drove down to the Keys in November 2004, it was absolutly fabulous. Just as you have drove through Key Largo ( a few miles) there is a place on your left called the Theatre of th sea, where you can swim with the dolphins, watch the Manatee's in their natural habitat, watch dolphin shows etc. Also there is the John Pennicamp Nature Reserve actually in Key Largo, where you can go on a glassbottom boat, go scuba diving etc, i would recommend the boat thing, its great, i would suggest a night or so at Key Largo as there is a fair amount to do, and it is so relaxing, you may just want a day round the pool doing nothing, any other questions you need answering just let me know, as we spent quite alot of time here, and down at Key West (an amazing place), where are you staying? I will also be able to recommend some place's to eat.
Take care,and i hope this helps
Ali