I've really enjoyed Bethwaite's books including "Higher Performance Sailing". Down side is that they read a bit like a college textbook and is focused more on 18footers, 49ers and the like. However, after reading them I've found those boats tactics/strategy are very similar and it is chock full of how's and why's which have really helped me better understand the nuances of getting the most out of our boats.

Recently read "Assymetric Sailing" by Andy Rice. Good book, but not sure if its worth $20.