All of the above are good recomendations you should also try a pattern called a "Kwan". When I asked about what flies to get when I was in fly shops down there last time, that was all I saw. Crab patterns of any kind are always good. If you are wading on the Atlantic side a Gotcha or Charlie may work but the fish in the Keys see a lot of flies. If you want to catch a tarpon fish around any of the bridges at night on the outgoing tide. Don't fish from the bridge but rather fromt he shore along the sides. Bring a stripping basket and some waders, it gets a little hairy wading in the dark with just wading shoes on down there. No telling what is swimming by.
Make sure you stop by Bonefish Bob's in Islamorada. it is right next to Sandy Moret's. Bonefish Bob's is where I actually got good info on where to fishthe last time I was down there too. They didn't just try to sell me something. Good luck and have a great trip.