Old timers may remember Byte magazine, and Steve Ciarcia's column therein. Steve went on to publish Circuit Cellar magazine, an electronics magazine which is more or less dedicated to embedded computer systems. Byte books published a book of his called "Build Your Own Z80 Computer", which now can be downloaded in its entirety with Steve's Permission from scribd or Google Books.
Why would anyone want this book? After all, the Z80 is pretty primitive compared to even microcontroller chips like the Atmel ATMega series or PICs. For me, it's a return to my computing roots; a chance to do something that I couldn't do back then. Z80 parts are still available and inexpensive, and you can still learn a lot about computers by tacking one of these things together.
Build Your Own Z80 Computer.