Some Alternate Reality Games you should investigate:

26 Learning Games to Change the World A number of the games above are included in this article but their are many, many more games listed. Check it out!

Larry Ferlazzo's Best Online Learning Games of 2008 - A listing and short explanation of Larry's top 20 picks for 2008 in reverse chronological order.

101 Free Edugames from ZaidLearning

Do you have others that you'd recommend? Please feel free to add them above.