I tip $3 or $4.
I can say, as an ex-pizza delivery person, that you guys are VERY generous compared to most of the people that order! Thanks! Driving pizza to someone's house may not seem like tough work, but I was always more wiped out from that job than from any of the waitressing jobs I had, and those always paid out a LOT more in tips. (However, in most places pizza delivery drivers do make minimum wage, unlike waitresses.)