The Hello Android book from Pragmatic Publishers is pretty good (a substantial but easy sample project). The official Android docs are excellent, see in particular the many example projects.
Reto Meier's Professional Android book is my favourite more advanced reference and guide. A lot of it is much clearer than the official docs (I found it particularly useful for understanding widgets, something, at the time at least, the official docs did a terrible job of).
Android Asset Studio is a nice way of quickly generating custom themes for your app (use with the Android KickstartR and Action Bar Sherlock for impressive Android 4.0 themes which work on older phones too).
Android 4.0+ and iOS 7+ Only
Why I don't think it is worth supporting Android < 4.0 or iOS < 7 on new Apps.