Valve and Dark Horse are teaming up again, but this time they are working on The Art of Portal 2. This is a 184-page hardcover book that features lots of concept art, character renderings, and comments from some of the developers on the game. The Art of Portal 2 will be released October 31 of this year, and no price has been set as of yet. But given the quality of their last book The Sacrafice and Other Steam-Powered Stories, this one will be worth any price. Kotaku has a couple of other exclusive images, so head on over to their site to view them all.