Recently on the iTunes App Store for the iPad, there was an app released called "The Final Hours of Portal 2". This app is an interactive book, if you will, for the iPad. It provides you with back story on the developers, and the processes behind the making of Portal 2.
You get a pretty good look into the backgrounds of the developers of Portal and Portal 2. It also delivers a great interactive experience. There are polls, photos, and videos. There is so much jam-packed into this app. Some may argue that content like this should ship with the game, but for $1.99 you won't find any complaints from this gamer.
To pick up your own copy of this app, click here and enjoy.