Our current favourite book is Beginning Android Application Development (Wrox Programmer to Programmer) by Wei-Meng Lee.

This book is aimed at those who are already comfortable with programming, but want to quickly get up to speed with developing for Android.

Beginning Android Application Development:

• Explains what an activity is and reviews its lifecycle
• Zeroes in on how to customize activities by applying styles and themes
• Looks at the components of a screen, including LinearLayout, AbsoluteLayout, and RelativeLayout, among others
• Details ways to adapt to different screen sizes and adjust display orientation
• Reviews the variety of views such as TextView, ProgressBar, TimePicker, and more
• Covers SMS messaging and networking
• Walks you through how to create an Android Service and interact with it
• Pares down the most essential steps for publishing Android applications

All in all the book is a really good read, and will probably sit around as a reference once you have read through it.

The only downside is, as with all fast moving industries, the book is likely to become out of date fairly quickly.