That's great! Here's some ideas for you!
Soup and biscuits -- make a big pot of soup or stew, and make cheesy garlic biscuits (the recipe is on the bisquick box). Plenty of food for everyone, and darned tasty. If you want soup recipes, drop me a line.
Garlic Chicken Goodness http://www.livejournal.com/users/kittenpants/55523.html
-- double the recipe and make it in a big rectangular casserole pan. Cut into eight servings and serve with risotto and a salad.
Also, remember that Thanksgiving isn't the only time you can make a turkey or a ham! Add mashed potatoes and a salad and you're in business.
Tacos -- make a big batch of seasoned meat, beans, rice, and get a bag of shredded cheese, some lettuce, a can of sliced black olives, some sour cream, salsa, and tortillas -- let people fill their own.
Breakfast for dinner! Pancakes, scrambled eggs, and sausage
Go get a copy of Joy of Cooking
. It is literally the only cookbook you'll ever need. Also check out OAMC websites ("Once A Month Cooking" or "Freezer Cooking") -- they have lots of recipes scaled to serve 8 people or more!