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.
* 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.
* Andrés Martínez Quijano’s ‘Greg‘. This one is a bit harder in that you are on your own. Once you figure out just what you have to do to go further (assume you’ve been given all the information you need), he guides you through the process as an ingame narrator of sorts. I think it works because you get to see just what it is like to play an ARG: you start off not knowing if it is one or not, and find ways to figure that out and to find out more. Andres has just emailed me letting me know he has created a post-mortem. It will be up at the ‘what is an ARG?’ section of the IGDA ARG SIG site shortly, but in the meantime you can download the pdf of Greg: A Sample ARG by Jengibre Interactive here [pdf].