In addition, Castle Hill, The Mooring, 22 Bowens, The Spiced Pear, Fathoms (at the Marriott) will all be serving on Thanksgiving. If you are looking for a lively scene, I'd pick the Cooke House, Mooring, or 22 Bowens.
We go to The Mooring every year. Thety serve a traditional turkey dinner but the regular menu is also available. The food is consistantly delicious and the service is good. It's also a beautiful restaurant and it's nice to sit close to the fireplace on cold nights.