Simply, the best introductory book into electronics you can buy. Inexpensive, detailed, and easy-to read. Get it! Get it now, now, now!
Absolute Beginners Guide to Building Robots By Gareth Branwyn. Get the parts for the project robots too!
Intermediate Robot Building by David Cook covers all aspects of robot building, from mechanical, to electronics, to microcontroller selection
Create your own Arduino-based designs, gain in-depth knowledge of the architecture of Arduino, and learn the user-friendly Arduino language all in the context of practical projects that you can build yourself at home.