Fro those who have never played an ARG and are interested in understanding them more, here are some sample ARGs.
* Dave Szulborski‘s ‘Errant Memories’. A game Szulborski created for beginners. He takes you through the whole process, explains what do in his two books: This is Not a Game, 2005, pp. 343-377 and Through the Rabbit Hole, 2005, pp. 105-132. Szulborksi is a highly regarded ARG designer and the books are an excellent introduction (the only ones around!) to the genre.
* John W. Gosney’s ‘Route 66’. Like Szulborski, Gosney guides you through the steps in his book Beyond Reality: A Guide to Alternate Reality Gaming, 2005, pp: 105-180. It has a strong pedagogical angle in that it can be used in classrooms.
* TJ Jackson’s ‘Troy’. It is a small game located at the IGDA ARG SIG site. You can play it and read the post-mortem which explains the process and how it was created.