Saw this today on Serious Eats. Brilliant. "Need" this. After dreaming of a wood-fired pizza oven, this may have to do. Pricey at $79.95 + shipping, but it comes with a thermometer, which would be handy even when grilling other things.
The Pizza Kettle ($79.95) is an aftermarket insert that turns your Weber Kettle grill into a sort of coal-fired pizza oven. It basically "extends" the height of your grill enough to give it an oven mouth that you can slide pizzas in and out of. The lid stays on, with the idea being that the temperature stays high enough inside to cook the pizzas under the same intense heat that the best wood- and coal-fired ovens reach.