Seriously, if you haven't had Maffei's... best pizza in NYC, hands-down. They've perfected the "Grandma slice," and I don't think I'll ever have better.
Downside: Don't expect to eat there. During lunch it's packed with people, sometimes a line outside... take-out is the way to go. I was at Law & Order one night late, and they ordered from here... I'll never find better! (Except, well, that one place in Milano.) :-)