Just went to a place called "Campo di Fiore" in the Holyoke Center arcade in Harvard Square (the same building as Au Bon Pain). It's a high-volume lunch spot (take-out and food court-style seating) with surly staff, but they do have really delicious food.
They sell a variant on pizza that they call pani romano, or "roman bread." It's essentially pizza, but in the dimensions of one of those superbowl party sub sandwiches -- very long and narrow. The crust is the centerpiece of this stuff -- it's very crispy, chewy, and tasty. A square piece of the pre-made pie that you choose (there are seven or eight varieties) is reheated, cut in half or in quarters and then assembled like a sandwich.
Prices are rather high for what you get (they've basically found a way to make you pay $7 for what would otherwise be two small slices of pizza and a small soda), but it's tasty enough that I don't mind.
Go for the varieties without cheese -- I find these to be better than the more traditional pizza types.