I sailed back in the late 70s and early 80's, then mostly stopped for a number of years. Recently (early summer, 2011) got back into sailing with the UCI Sailing Club. While I was "gone" the sailing world has changed a lot in some areas, and not at all in others.
My co-worker lent me his book "High Performance Sailing" by Frank Bethwaite, and it was an eye-opener. Reading the book helped me gel some ideas about sailing that have been rattling around in my head and inspired me to attempt to put together information in a useful way.
Frank's book is organized like a pyramid, with basic information first, leading to conclusions about how to sail later. After extensive page flipping, I read the book backwards, starting with his tips on sailing and working back to the earlier chapters on wind and water.
I've read several, maybe 30 or 40 books on sailing. Of these three have really inspired me. One was "Start to Win", by Eric Twiname. Start to Win is focused on dinghy sailing and really emphasizes prioritizing attention. There are way too many things to think about when sailing, and figuring out which to focus on is a major success skill. Eric points us in that direction.
The second I only recommend for the True Nerd: "Aero-Hydrodynamics of Sailing" by C.A. Marchaj. Marchaj brings out a number of technical ideas and explanations, in a form only a tech person can love. His book offers lots of great diagrams and wind tunnel work that help in understanding basic phenomena, and is a great technical reference.
The third is High Performance Sailing. Frank Bethwaite. Frank offers TWELVE chapters on wind. Turns out he is an atmospheric scientist as well as a sailor and pilot, so he has lots to share on the subjects of air, air movement, and boat propulsion. What's really great about this book is that it is mostly pretty easy to read. Occasionally his weather descriptions get a little complex, but we are talking about complex things. He never loses track of how what he's talking about relates to sailing.