Columbia on Sand Key. Try the 1905 salad.
It's on the bay side of the water and is great for lunch or dinner. It's my go-to place when meeting up with friends who are visiting the Tampa Bay Area.
For something a bit more upscale, retro try Heilmann's Beachcomber. As you're coming off the roundabout from the mainland go right instead of left. It's down a few blocks on the right side. Valet parking available, too and that's important in that area. I was just there for Christmas Eve dinner.