So far as I'm concerned, the grandest of the lot is The Breakers in Palm Beach. Its Web site is here and the Wikipedia entry here.
Not so grand, but about as old and still pretty nice is the Don Cesar on St. Pete Beach in the Tampa Bay area. The Wikipedia entry is here.
In Coral Gables, near Miami, is another 1920s grand hotel, the Biltmore, whose Wikipedia write-up can be found here.
Below are some photos I took. No thorough studies here, just snippets to provide a taste.
Originally this room was the main dining area, but has been a bar for years. It was recently redecorated, perhaps with too large a dash of contemporary feeling.
A close-up of the bar itself. The illustration is mid 1950s, but I don't know who did it. Nor do I know if it dates back to then or is a retro piece.
The Biltmore has a huge pool. This was taken from the bar area.
Another view of the pool and main hotel structure from not far from where the previous photo was taken.