1. Anna Maria Island, Bradenton, FL is one of the most beautiful beaches I have been to. There is public access all over the island, and also public parks, one of which at the north tip of the island where you can see the sunshine skyway bridge. Holmes Beach is also nearby and here's a pretty nifty site with some places to find.
2. Fort Desoto Park, Pinellas County, FL is an interesting park with a little bit of Florida History. There you can camp very close to the beach. Egmont Key State Park is also nearby and has beach access as well, just no camping there.
3. Honeymoon Island State Park, Pinellas County, FL (north of Clearwater and west Dunedin) has beautiful beaches remaining in their natural state with rocks and shells along the shore. This state park doesn't allow the removal of it's shells to retain the natural beauty of the beach. While I visited the park, dolphins were swimming very close to the shore. There is a cafe, playground area, and access by ferry or private boat to Caladesi Island State Park. Go to my picture album here to see my pictures of Honeymoon Island.
4. Clearwater Beach, Pinellas County, FL an island off the coast of St Petersburg, has beautiful white sand beaches and Pier 60 where there are different attractions at night. There are also lots of shops and restaraunts to visit on the island. Don't forget to hang out with the pirates while you're there.
5. Sanibel and Captiva Islands, Lee County, FL has beaches you are allowed to "shell" on (collect shells and take them home). There also is a lighthouse on Sanibel island, and a pier.
6. If you love lighthouses, Here is a listing of the lighthouses in Florida.