Directory of Educational Resources on the Web (Teaching & Learning Resources)
If you are willing to consider an Android phone, Georeader is a great history app that students can contribute to and learn from. They can also use the website to participate if they don't have a phone. www.mygeoreader.com
I recommend this Timeline Eons app, a graphic representation of the entire natural and human history:
http://itunes.apple.com/us/app/timeline-eons/id433352152?mt=8&ls=1
ohostetter
I would also add Westward Expansion app, Early Jamestown, Pass the Past, and World Book This Day in History apps to your list. Thanks for sharing your app lists online.