I've lived just down the street from Mamma Mia's for almost 3 years now, and it's been my favorite pizza place ever since I discovered it. The prices are just right (two slices and a drink is enough to fill anyone up, and it's only around $5). The owner (Frank) is friendly and always remembers my name when I come in, even when they're crazy busy!
Added bonus: Immediately next door is a small alcohol store where you can grab some beer (if you're getting your pizza to go). And what goes better with pizza than beer?
The only downside I've noticed is that their full-size pizzas tend to be somewhat limp in the middle. I always get slices (which are cooked by themselves), so that's never really an issue for me.