For a hundred dollars, which is only £60 so entirely comparable to other CEs you get:
Special edition box containing both the game disc and a DVD or Blu-Ray of the documentary, Double Fine Adventure Backer T-shirt, original "Double Fine Adventure" poster (suitable for framing), special thanks in the game’s credits, and all previous reward tiers. (These items are exclusive to the campaign and will be shipped for free in the US. Please add an additional $10 to your pledge for international shipping)
PDF version of the Double Fine Adventure Book (filled with 100+ full color pages of concept art, original photos, developer bios, excerpts from the game’s script, deep dark secrets, and more!), and all previous reward tiers!
HD download of the documentary series with extras, Digital game soundtrack, Digital documentary soundtrack, and all previous reward tiers.
The finished game in all of its awesome glory DRM free on PC, Mac, and Linux, or via Steam for PC and Mac, exclusive access to the Beta on Steam, access to the video series, and access the private discussion community.*
That is basically a cracking deal for anyone interested in the game. This is probably one of the most exciting projects that I'm following now.