A result of Android's enormous popularity is the increase in books dedicated to the OS. Two that we want to highlight at the moment are The Complete Android Guide, by Kevin Purdy of Lifehacker and My Droid by CrackBerry's own Craig James Johnston.
Purdy's book just went on sale and can be bought for $19.95 (paperback) or $9.95 (DRM-free E-book) [CompleteAndroidGuide] Purdy also created a Twitter handle called @completeandroid, which will provide tips periodically to its followers.
Johnston's book is available for pre-order from Amazon for $16.49.[Amazon]