An excellent book published in 1987 for Radio Shack by Forrest M. Mims III, this book was my first introduction to electronics. At the age of ten, I pulled this book off the shelf, begged my dad to buy it for me, and proceeded to tear apart anything and everything that was electronic and broken - and some stuff that wasn't.
To begin with, this book is no longer sold by Radio Shack, but is available from http://www.forrestmims.com. I'd strongly recommend it to anyone of any age who wants to understand the idea behind all this electronical stuff - it's written notebook style, on lined paper, and looks like freehand text and drawings. Keeping in mind that this is written from my (fond) memories of this book, I'll continue.
The book opens with a general introduction to electricity (both static and otherwise), and continues with how to make your own power source out of a lemon (or other citrus fruit) and a few strips of metal. After that, there's explanations of electromagnets, which is fun to actually put into practice, albeit a bit dangerous with a sufficiently strong power supply. Following are explanations of all of your most common electronic components: resistors, capacitors, transitors, transformers, assorted gated semiconductors, diodes, and best of all, the 555 timer, as well as some guidelines on identifying them. All of the sections are done with amusing yet informative drawings, making this look almost like a sketchbook at times without detracting from the information.
The final section of the book, which is about 128 pages long in total, is devoted to a plethora of simple electronic circuits you can build yourself with a minimal outlay of cash. Building the circuits and actually examining how they work will give the reader a good understanding of not only reading schematic diagrams (an important skill in the electronics field, IMHO), but also an even better feel for how the components work within a circuit. I'd consider this an excellent investment for anyone looking to get into this field.
The interesting part is, this book was also a part of the study materials for my course in basic electronics for the United States Marine Corps in 2001. Even after 14+ years, this book was still an excellent and pertinent reference.