Happy Joe's is absolutely fantastic, but I think it's really its own style of pizza.
Actual "Quad-Cities" style - the oblong slices, thin sauce, finely-ground sausage, toppings under the cheese - I'd say doesn't get more definitive than good old Harris Pizza. As I remember, there's two in Davenport, one in Bettendorf, and one in Rock Island.
I also seem to recall a "Fat Boy's Pizza" on Washington Street in Davenport that made a pretty good pie, but I think I last had them when I was in junior high school and my memory can't be trusted. Not sure if they're even still there.
post edited by Ketteract - 2011/10/10 00:03:09