A pizza peel is a large, flat paddle with a long handle, made of wood or metal. It is used to transfer both your uncooked and cooked pizza in and out of the oven. If you are using a pizza stone (rather than a pizza pan), you'll find it indispensable. Look for a sturdy peel with a handle long enough to get your pizza in the oven without you getting burned (at least 8 inches is best). It should also have a work area large enough to easily hold the size pizzas you want to make, generally a 14 by 16 inch square surface. Finally, a hole in the handle gives you the option of hanging it, especially nice considering that it can sometimes be tricky to find a good place to store it if you have limited space in your kitchen.
I prefer a wooden peel to a metal one for a couple of reasons. First, the pizzas seem to move around better on a wooden peel, with less sticking to the surface. And second, you don't have to worry about the peel getting too hot and possibly burning you, as can happen with a metal peel. Just be sure to oil your peel every so often to keep it from cracking, and, as with all wooden kitchen tools, don't leave it soaking in water or it will develop cracks. Here are some tips on using a pizza peel.