Books I own, and that I have any opinion on. Of these I’ve had the most use of Practical Arduino. Example code is available for all.
There are more books coming out weekly now, so it’s clear especially Arduino has become a huge success among hobbyists and professionals.
A good starter book with lots of practical examples, where some are rather complex.
Making Things Talk
Primarily covers wireless communication and location for Arduino, with a few sensor/control examples. This is not an all-round project book.
Getting Started with the Internet of Things
Focusing almost entirely on using Netduino to communicate with Pachube. A good starter for that, as the documentation at Pachube is rather opaque.
Amazon sells both board families and lots more books than mentioned above: