Where can I find Android's default icons?
\path-to-your-android-sdk-folder\platforms\android-xx\data\res
you can use
android.R.drawable.xxx
(use autocomplete to see whats in there)
Or download the stuff from http://developer.android.com/design/downloads/index.html
You can find the default Android menu icons here - link is broken now.
Update: You can find Material Design icons here.