Howdy,
It's a nice drive down into the Key's I should know have been down in the Key's numerous times, just be careful and obey the speed limit as FHP and local Sheriff's like to ticket speeders.
The main points that stand out in my mind Islamorada nice little town to stop pick up a few souvenirs stop by the chikki hut get a drink and walk around the dock there's always fish waiting to be fed behind the bar there's a nice little beach and a fresh water pool.
Stop in Big Pine Key (they enforce the speed limit that's posted) and check out the Key deer they are protected by state law so don't get caught feeding them or trying to touch them just drive down one of the gravel side roads and you'll see the Key deer. Don't know the name of the salt water pond that's in Big Pine ( just ask a local they'll head you in the right direction) its really clear and you can see all the tropical fish, sea turtles and barracudas floating around in the pond there in a salt water inlet to the pond.
Stop off by the 7 mile bridge there are parking places along the road take a dip in the Atlantic and then walk across the street and take a dip in the Gulf.
Key West is nice rent a scooter and ride around the town check out the sites Mallory Square is nice about sundown all the freaks come out @ this time this is very cool, stop and have your picture taken @ the southern most point of the US of A.
The tourist traps Hogs Breath Saloon, Ricks Cafe 6 bars inside, MargaritaVille you'll definitely not lack for things to do...
*Fantasy fest is really cool during Halloween there are so many people on the island that you can't move everything from A to Z have done Fantasy Fest the past 4 years in a row and plan on going again this year.
*oh yea if you stop in for a drink @ some of the motels don't be offended by nude people walking around as pretty much anything goes down there in Southern Most Florida.
HogLeg