Many of the beachfront hotels can and will do this. We have a couple of places that we partner with frequently. One is highlighted on our blog at http://www.simpleweddingsblog.com/2011/04/st-pete-beach-wedding-and-reception.html. Another place I have in mind is an exclusive private beachfront residence that will seat up to 25 - you'll have to contact us for details on that one (actually, I see you already have - be sure to ask April about this option!).
We also have some places that aren't right on the beach, but are just a short walk - so you only have to park once and your guests can leave the wedding and walk right to the reception. The Black Palm on Pass-a-Grille is our favorite in this regard. They have a stunning outdoor courtyard that can seat up to 80, and have indoor options as well.