If it's not too formal, I'd probably make a big pot of chili or two, a couple loaves of bread (frozen dough is easy, and fresh baked bread impresses the hell out of people) and buy a couple of those pre-cut vegetable trays at Costco.
Alternatively, a bunch of boneless chicken breasts - grill 'em up, slice 'em, and serve them over a bed of spinach with some feta cheese, dried cranberries, nuts, and sliced tomatoes.
And booze. Lots and lots of booze.
A second on the chili. Pick up a 5lb chub of ground beef, a couple pounds of pre-diced onions, 3 32oz cans of diced tomatoes, 3 normal cans of crushed tomatoes (or tomato paste), 3 32 oz cans of kidney beans, 3 cans of black beans, and about 4-6 cans (usually I can only find the little half height cans, if you find the full size you only need 2) of mild/medium green chile (I highly recommend Hatch New Mexican green chile.) For seasoning salt, pepper, cumin, red chili powder
For each pot brown 1/3rd of the beef with 1/3rd of the onions, add a can or 2 of green chile, a can of diced tomatoes, a can of crushed tomatoes, a can of kidney beans, and a can of black beans. Add seasonings until it tastes good.
I would do corn bread with it, you can pick up 3 boxes of cornbread mix, and cook 3 9x13 pans. Toss up a couple bags of salad mix with pre-sliced mushrooms and cherry tomatoes, and you're done.
The cornbread can be cooked in advance and refrigerated for one or two days (seal it well to keep it from drying out) and then just warmed up in a 200deg oven. I suggest cooking 2 pots of the chili in advance and putting it in disposable foil containers in the fridge. Make the 3rd pot the day of the party, then put that in a serving bowl, and dump one from the fridge into the pot to warm up. If you have a crockpot even better for keeping extra chili warm.