We just returned from a week in Largo, and I would not miss Mandalay's on the oceanside. Small, charming, and right on the ocean Mandalay's has great sauteed conch steaks w/ key lime butter. Also great were the sauteed grouper sandwiches, much better than the fried FWIW, the oysters, and a great not sweet and just tart enough key lime pie.
Our other favorite is Calypso, also in Largo. Small, family run, but without the view. It serves great she-crab soup, fish tacos, hogfish sandwiches, deepfried corn, and fantastic sangria.
Jim