When I head down to Disney, I always have sit down dinners. By far the best, but it is more of an event than anything else, is Victoria and Alberts in the Grand Floridian. If you are not going with kids, and you want to have a nice quiet romantic dinner and TAKE YOUR TIME having it. This is the place for you. They either have one or 2 sittings a night, I think one at 5 and the other at 8:30 and it is a five couse meal, the menu being completely market driven (whatever comes in THAT day) and being very short on selection (1 - 3 items per course). But it is truly ecquisitely prepared. With the wine paring its $135 per person, pricy but so worth it. And you never forget it, in fact you get your own personalized menu and ladies receive a rose.
Regular sit down resturants, I have a toss up between Artists Point (WL) or the California Grill. Both are excellent with Artist Point having Northwest American cuisine (try the bison steak with the sweet potato gratin, mmmmm) and wines, and the Cali Grill with Pacfic Rim cuisine.