Do you want party food (snacks/finger food) or an actual meal?

Finger food is easy...things like chips with salsa/guacamole/bean dip, hummus with flatbread and vegs for dipping, finger sandwiches with whatever fillings you like, veggie sushi, pretzels, cookies, etc.

If it's an actual meal, I think Italian or Mexican food are easy to make veg*n without omnis thinking it's too weird.

Mexican: veggie and/or bean enchiladas, Mexican rice, a build-your-own taco/burrito bar with beans, lettuce, tomatoes, salsa, guacamole, peppers, olives, etc. (and tortillas/taco shells, obviously).

Italian: pasta with a good tomato sauce (either plain or loaded up with vegs), big salad, garlic bread and/or bruschetta

Eggplant* and Pasta!

peel and salt eggplant for 30-45 minutes.
rinse it off and marinate it in smoked paprika, olive oil and pepper for 30 minutes
bake at 400 degrees for about 30 minutes--until soft (make sure to flip them around a couple times)
while the eggplant is baking make the sauce** and boil the pasta

*if you prep the eggplant right and remove all the bitterness the eggplant wont really change the taste of the dish but will add a creamy element and I think omnivores wont miss the cheese this way

**I just use one standard size (14oz?16oz?) can unsalted diced tomatoes, one 6oz can tomato paste, on tomato paste can of veggie stock, and as much salt, pepper, basil, oregano, and thyme as you want--then the most important part... extra virgin olive oil. adding oil makes the sauce turn out more... i am not sure creamier, smoother, tastier. I like a lot (1/3 c!) but however much you like would work fine, just add some. you obv could just buy some sauce but this is a bit tastier because too many sauces have added sugars which i find ruins the taste.

More foods:

http://www.wholeliving.com/recipe/vegetable-tartlets (replace ricotta with tofu, nut cream, etc)

http://www.tasteofbeirut.com/2008/11/how-to-make-pumpkin-kibbe/

bake nice hot delicious soft fluffy bread and serve some spreads with it (nut pate, hummus, baba ghounush, herb "butter", etc)

id stay away from faux meats (noticeable tofu included) and not a TON of beans. a lot of omnis dont eat beans regularly and it could cause some discomfort

and if you want desserts...
http://www.wholeliving.com/recipe/lemon-cream-with-blackberries (just replace the honey with something else... Ive tried it and it is really good and light)

i would stay away from fake meat and vegan cheese with non vegans, keep it is "normal" as possible...

veggie burgers and fries

vegan potato salad

7 layer dip

roasted or grilled veggies

hummus and crackers

veggies with thick homemade vegan ranch

veggie fajitas or burritos

kabobs

vegweb's cheesy bean and cheese enchiladas

veggie lasagna

  These are great suggestions.. When I go to parties I always search out the healthy appetizers and even at omni parties, there always seems to be crudites and dips, so go with those and they'll feel comfortable immediately.

And to all the other GREAT suggestions (are these people wonderful or what) I would add that you consider one of the recipes here for some sort of lentil, nut, rice loaf that can be served sliced, coupled with a tasty mushroom gravy. Or maybe a hunter sauce made of cherries or berries and wine.  Some grilled or roasted veggies for a side or individual stuffed and broiled tomatoes, or maybe homey "mac n' cheez".  Whatever, you'll find something here and it WILL impress and please your guests,

Have a wonderful time.

make your own "Gyros"- big party hit
but first youll need field roast-
Do you have access to whole foods?

also everytime i make hummus pizza its gone baby gone before i even get to have any-
easiest way: prepackaged pizza dough, hummus of your choice, spinach,and caramellized onions.
                   -thin slice a ton of onions, about two big ones for one pizza, add to pan with olive oil and caramelize on medium, takes about 30 minutes then add fresh spinach couple of hand fulls, cook till whilted. spread out dough on pan and cook to directions(about ten minutes) till just done take out of oven, then transfer to serving pan and spread thick layer of hummus over whole pizza. then top with onion spinach mix. can be served hot or cold great both ways!

please let me know if youd like the "gyro" idea-its amazingly good simple filling and easy for guests to put together themselves!