Monza, at 451 King Street just south of Radcliffe Street, is my favorite pizzeria in the US. Not that I have tried them all, but I do not remember one nearly as good from my days in NYC, and have not yet found that comes close in Washington, DC. It is close to Northern Italian style, so the crust is a bit harder than Neapolitan style, or so I am told.
My only grievance is the names (Materassi for the basic Margherita, etc.) — just read the descriptions.