I don't know if I can pick just one...
I usually like to snag the skin off the turkey. Barbaric, but oh-so-good. But that's just *part* of a dish...
As far as a single "dish" that I like the best... I'd have to say the seven-layer salad. It's so simple, but so good. Lettuce, celery, water chestnuts, green onions, hard-boiled egg, bacon bits, peas, and a garlic-onion-mayo-sour cream concoction of dressing. The M-I-L is an awesome cook, so we usually do thanksgiving at their house. YUM.
Also, one cannot discount the usefulness and deliciousness of "leftover sandwiches." But again, technically, that isn't a Thanksgiving dish. That's a day-after-Thanksgiving gorgefest. Pile the leftover turkey, stuffing, gravy, and--if you're adventurous--some of the contrasting vegetable sides, onto a day-old Thanksgiving roll. Heat, eat, and be full. Or just nosh it down cold.