First of course is the what WikiPedia has to say:http://en.wikipedia.org/wiki/Android_%28operating_system%29
A mobile operating system running on the Linux kernal.
The main site:
http://www.android.com/
The developer site:
http://developer.android.com/index.html
Example of an application. This site has several articles:
http://www.linux-mag.com/id/7633/2/
