Hi Devora, great to hear from you! I find that Pinot is the best pairing for the huge diversity of the dishes that are thrown down on the table for Thanksgiving, much like SSJakira1 mentiones below. It usually has a medium body and great acidity, all of which go well with food. Try the 2006 Lucienne Santa Lucia Highlands Lone Oak Vineyard Pinot Noir, for instance.
For the post roast, I'd go bigger so that you can better pair with the heavier and darker meat and fats you find in a tasty pot roast.  Try the 2006 Titus Vineyards Napa Valley Lot 1 red blend.  It's an unusual blend of two powerful varietals, Petit Verdot and Petite Sirah.  Tasty stuff and can handle any full flavored meat that you send its way.
Lastly, and perhaps the most fun, try bubbly!  Sparkling wine can fit the festive mood and pairs with almost everything, including that big pot roast, because of it's high fruitiness and acidity and low alcohol.  I'd go for the non-vintage Amarosa Bella Mendocino County Brut Rosé, which has some sexy color and texture due to the rosé style of the vinification again, from Pinot Noir.  Cheers!