I have been experimenting with this method lately, and I am warming to it. (ha-ha)
I use a microwave. It tastes much better in a toaster oven or the big oven, but I’m lazy. And when hungry, impatient.
Cold is the best way to eat left over pizza followed by the covered skillet if for some strange reason I want it warm.
…That says “By your Command”
I answered “toaster,” meaning “toaster oven,” but, in all honesty, it always gets eaten cold. Or room temp (leftover pizza rarely finds its way into the fridge in my house.)
This is also a toaster. Also not good for reheating pizza.
I reheat leftover pizza in the oven (because I don’t own a toaster oven). The microwave oven is faster, but the pizza gets soggy that way. But good pizza is good cold. Bad pizza isn’t good even when it’s fresh.
I use a sandwich press, just leave it cracked so the top is a cm off the top of the cheese.
Cast iron skillet on the stovetop is the correct answer.
It’s not worth it to re-heat something I will spend less than a minute eating
- don’t own a toaster
- toasting shit dries it the fuck out
- I prefer greasy warm pizza to either dry as fuck pizza or cold pizza.
suck it! 
I’d always reheated pizza in the oven (400 degrees for 9-10 minutes), but I saw Tyler Florence recommend a skillet on one of his Food Network shows a few years ago. It works pretty well, as long as you’re careful to make sure you don’t burn the crust before the toppings get warm (I’d not thought of the “flipping” technique that Athena suggested – I’ll have to try it).
I don’t like what microwaving a pizza does to the crust, so I avoid that technique.
Other: Non-stick pan on low, covered. 5-6 minutes.
–This begs the question: At what hour and moment does Friday night’s party become Saturday mornings breakfast?
Am I the only one that has ever gotten her tongue pinched by the crust in the reheated by oven scenario? What kind of freak am I??
Toaster oven. 350 for about five minutes, makes it perfect.
I tried a little frozen pizza, which had directions for oven or microwave. Oven took too long, microwave was disgusting.
Leftover pizza? You’re just not trying - there’s always room for that last slice. 
Toaster ovens are not made to make toast. They make rotten toast. They are made to heat sandwiches and re-heat pizza. I do not have a toaster oven. I tend to eat it cold (room temp) but will sometimes nuke it to make it warm.
one cannot make decent toast in a toaster oven, it cannot be done.
The correct answer is frying pan and toaster. Works for frozen pizzas too. Heat up in dry frying pan until you smell nice toasty pizza base. Then under the grill to do the topping.
I’ll do this when I’m not in a rush.
When I’m impatient I zap it before it goes in the pan, or just eat it cold.
A quarter pat of butter or a few drops of olive oil in the skillet do very nice things for the crust.
Athena’s flip technique sounds interesting. Might be the wave of the future.
Mr. Rover: yes, using a skillet dirties a pan and spatula, but the spat doesn’t need rinsing before it goes in the dishwasher. And cleaning a non-stick griddle is easier than getting spilled topping out of a toaster oven. Using oil eliminates the butter knife.