• Embedded Microprocessor Systems: Real World Design, Third Edition
• Designing Embedded Hardware
• Programming Embedded Systems: With C and GNU Development Tools, 2nd Edition
• The Circuit Designer's Companion, Second Edition (EDN Series for Design Engineers)
• Embedded Systems Architecture: A Comprehensive Guide for Engineers and Programmers (Embedded Technology)

A helpful reference
Review written by: Michael Barr From Elkridge, MD USA
I keep this book on my office bookshelf. With its coverage of all manner of I/O devices from sensors and actuators to timer/counters to stepper motors, it's come in handy a few times. Think of it as your reference to interfacing to the real world in which your system operates.