There are tons of recipes for texas caviar (bean salad this is eaten with chips) that pretty much anyone would find delicious and not "weird." I make a really good wild rice and asparagus salad with sesame oil and soy sauce dressing -- I'll post the recipe if that sounds interesting to you at all. Really, any kind of bean, grain, or pasta salad would be easy to make and not too suspicious to omnivores.
As much as I love vegan mac and cheese, I wouldn't serve it to a nonvegan crowd in general because it's never going to be quite the same as whatever their favorite mac and cheese is.
Vegan cookies always go over great as well.
Chocolate chip, or whatever you like! Of course I wouldn't recommend bringing only dessert if there isn't going to be other vegan food, but desserts are a great way to win people over.
Oh, and some good general advice, never plan to bring something you're just making for the first time. That's a recipe for disaster. Always do a test run, at least. Ideally, you want to have made the dish several times before its omnivore debut.