Cork Screw Swamp is a good birding location in Florida. They have a fantastic board walk through the swamp.
Ding Darling as mentioned above is a highly recommended site. When my wife and I went to Florida several years ago we went on a Friday and it was closed! So you may consider this and not go on a Friday.
Florida is probaby best known for its Everglades. This is a must see area if you are birding in that state.