There is a new Android SDK version out. I haven't messed with it, but thought I would put the link up. I think it is the future of the next wave of handheld device OS's.
http://code.google.com/android/what-is-android.html

This article here also gives a very nice other view to what Android is:
http://www.news.com/8301-13580_3-9815165-39.html

A nice detailed video explanation of the API, highly recommend to watch to get a lot of info