August Mueller's Pizza Lab writes about the adventures in making great pizza.

In this post back in April, he detailed the gear you should have when making pizza. Here's what was said about pizza stones:

If you like the types of pizza that I do, then you absolutely need a pizza stone (also known as a baking stone). The thicker the stone, the better (the stone acts as a heat sink and will cook your pizza from below using conduction). And the hotter you can get it, the better (I get mine up to 750° over the course of about 40 minutes- heat up too fast and you'll break the stone).

If you don't already have a stone, I'd recommend the Dough-Joe stones. I've gone through 4 or 5 pizza stones over the years (I really push a lot of heat through them, and sometimes too quickly) and the Dough-Joes are far and away my favorite yet (I've bought two sets in fact). They look a lot like "quarry stones" that you'll find mentioned on pizza blogs and forums, but they are much thicker and work better. If you already have a stone that's at least 1/4" thick, it'll work fine.