You can find the kernel at
http://git.android.com and the other
mirrored GPL and LGPL'd components at
Notices for other licenses can be found within the SDK.
Over time, more of the code that makes up Android will be released, but at this point, we have been concentrating on shipping an SDK that helps application developers get started. In short: Stay tuned.
One of the best explanations for the reasoning behind releasing code under Apache2 can be found in a ArsTechnica article by Ryan Paul.