I've thumbed through them all, and I keep thinking back to Hello, Android as the best place to whet your whistle on development. Make sure you know some java, basic familiarity should be enough, as I'm a sysadmin and could keep up. I'll be reading through OReilly's book in a day or two when it hits our library and I'll let you know what I think.
I started with sample source code(API demos) bundled with Android SDK 1.0 and learnt most of the stuff by looking at the examples. The Android developer Guide and API reference are the official documentation available(developer.android.com). You may also want to read blogs on the aforementioned site, these are must.
I also referred tutorials from anddev forum(some of these tutorials dont work with the new SDK though). Anddev is one of the oldest forums for Android.
There are 2 books, most of the folks like to recommend -
1. Hello, Android - Ed Burnette [Read JR Book-Review here.]
2. Busy Coder's Guide to Android Development - Mark Murphy
I have read Busy Coder's Guide to Android Development 1.0 by Mark Murphy and found it easy to follow.