We used to use the oven, or- horrors- the microwave. I read about this, and this is the only way I will reheat pizza, and even a few other things now. It's by Chef Anthony Falco:
1. Put cold pizza in a nonstick skillet on medium-low heat.
2. Cook 2 minutes or until bottom is crispy.
3. Add 1-2 Tbsp. water away from the pizza and turn heat to low. (I use 1 Tbsp. for one piece, 2 Tbsp. for 2 or 3.)
4. Cover and steam 1 minute, until the cheese is melted. 