I have equal affection for the dried out, reheated, next day slice and the piping hot, greasy, just-outta-the-oven slice. If I'm buying two for lunch, I'll usually take a reheated slice over waiting for the freshly made pie, but I can never tell if this is preference or hunger/lack of patience.
When I'm at home and eating a day-or-two old pizza piece, I have a little ritual I go through, if there's salad makings in the fridge too. Goes like this.
Broil the crap out of the cold slice - chop whatever greens and fresh veggies are lying around - mix 2 tbl balsamic, 1 dash garlic powder, dash salt, little blob of mustard, grind or two of pepper, shake well in a jar, add 2 tbl olive oil, shake again - plate slice, toss two handfuls of salad over slice - dress to taste (for me, it's usually the entire 1/3 cup, as described above).
It's like pizza casserole, but lighter. Lots of texture - hot, chewy, cheesy, crunchy and cool. Mmmm. And if you're a balsamic fan, the crust absorbing all of that tart, sweet goodness might get you planning ahead when you order pizza.