This 1997 release by Martin Russ is one of the best introductions to synthesis and sampling in print. It discusses both analog and digital synthesis concepts and sampling in a fairly non-technical fashion, making it a great way to expand your understanding of synthesizers.
Sound Synthesis and Sampling is extensively illustrated with diagrams that help make the ideas it discusses clear. The combination of layman writing and profuse illustrations help make some of the more difficult subject matter easy to understand.
Russ has written for Sound on Sound magazine, a publication known for its high standards and good writing. Russ brings a similar direct style to his book.
This book is highly recommended for anyone wanting to learn more about the basics of synthesis and sampling. This would also make an excellent textbook for teaching, because Russ provides timelines, examples of important/influential equipment, and even chapter reviews. Finally, he provides a large glossary of the jargon of synthesis.