Sharks Underwater Grill is the sit-down place in SeaWorld. We just ate there on Nov. 10 (we had lunch).
The room is lovely -- the tank is huge, and the tables are set up so that everyone has a good view. The food is pricey and they don't offer light options (I was really hoping for an entree salad that day, but no such luck). It's good, and it's always nice to be able to sit down and relax for a meal, but just know that you pay a premium (always the case inside a theme park!). You can find the menu on the SeaWorld web site.