This post is not for any grade, just something I felt was interesting.
There is an ARG for Portal 2.
There is a Steam Topic and a wiki discussing the game. On April 1, 2011, Valve released the Potato Sack which contained 13 indy games, including one that had not been released. Things in these games have been changed to have new levels, and references to Portal. In addition there is evidence that if people solve all the puzzles Portal 2 will launch early.