When I went looking for a beachfront hotel in Ft. Lauderdale late last year, I discovered that most of the hotels in Ft. Lauderdale are not on the beach--I found a total of four really nice hotels on the beachfront.
We wound up staying at the Pelican Grand Beach Resort, very nice, relatively new, and one of the few hotels on the beach. It is a bit off the beaten track. I can also vouch for Pier 66, which is on the Intracoastal and has a nice waterfront vibe. Both hotels are fairly pricy.