As a resident of South Florida, it is very hot here in summer. If you choose to visit florida beaches, I would suggest the panhandle - Panama City or Fort Walton Beach. Nice beaches, cooler temps.
The problem with the panhandle is it is typically expensive to fly into.

I would second the Cancun or Cozumel idea.
Skip the Bahamas, the price of food and drinks would kill you.

Myrtle Beach is fun in a campy Daytona Beach sort of way. And I hate to suggest it, but what about "the Shoooore" as the local Jersey folks call it. I found some of the beach towns entertaining. Though the fact that they charge to go on the beach was strange.