I like all of these and would add one myself that I stumbled on the other day - Gamebook Adventures: Temple of the Spider God. Good for decision making and risk taking as well as a great book for getting boys to read. Enjoy!
Read the full article: http://speirs.org/blog/2011/10/30/ambitious-ios-apps.html
See the list of Apps: https://docs.google.com/ambitiousappsspreadsheet