Here are a few ideas...
VICTORIA & ALBERT'S at the Grand Floridian. Undoubtedly, the fanciest, schmanciest restaurant in The World. Intimate, romantic -- candle light and the sound of a plucking harp are the order of the day -- and very VERY nice. Food is exotic, not to everyone's taste (venison, anyone?) but creatively prepared and presented. You receive a personalized menu to take home, and a rose (a nice touch!). Service is fabulous; each table is served by a pair of people, Victoria and Albert, who do everything to make your meal memorable. Not only is the food memorable, so is the price. Prepare to spend close to $200 for your meal.
JIKO at the Animal Kingdom Lodge is a close second, in my book. Lovely atmosphere, in a beautiful resort, with unforgettable food, seasoned in ways you would never imagine, but just plain great. (Try the tenderloin with mac & cheese. You can thank me later.)
ARTIST POINT at the Wilderness Lodge is exceptional, and a personal fave of mine, with some great Northwestern cuisine. The signature salmon is excellent. It's not THAT romantic, though. But it has a nice, woodsy atmosphere that would never EVER make you realize you were actually in the middle of the Florida swamps.
Bon appetite!