I was talking with my wife, she mentioed that a Snickers salad is always good. It throws people for a loop, they don't know whether to count it as a dessert or a salad. Having attended my fair share of pot-lucks and picnics, my Mount Rushmore of covered dishes would include: Tator-Tot Casserole, Broccoli and Cheese Casserole, Scalloped corn, and Hot German Potato Salad.
Please post a picture of what you come up with!