From the auction:
This ultra-rare Planescape sketchbook is part of an extraordinarily small print run, never offered in stores, available only at GenCon '94, and almost never makes an appearance on Ebay. Artist Dana Knutson has signed the first page. It comes from the library of Planescape designer Colin McComb.
The book offers a rare look at the early concept art of this award-winning AD&D campaign world. These pieces are accompanied by the notes of concept artist Dana Knutson, explaining the reasoning and rationale behind the decisions. Sketches include buildings, characters, weapons, armor, and monsters, and show the evolution of the trademark Planescape look.
Very cool
Ultra-rare Planescape Sketchbook - eBay (item 290282332965 end time Dec-21-08 10:33:44 PST)