Agree with Thataway...as usual.
Chapman Piloting & Seamanship is a great reference for all things boating, in my opinion. If you know everything in it, and apply it, you are more knowledgeable than most boaters out there.
Vigor Encyclopedia of Boating is very useful, in my opinion, and on Ebay.
Nigel Calder How to Read a Nautical Chart is a great reference.
Smart Boating with Capt Steve on 8 CD I have found to have tips and insights that I never knew or forgot over the years; I found we have been tying off cleats wrong (by only one pass) the past 25 years. Highly recommended for a reasonable price.
David Pascoe has opinionated, but free, dated crusty surveyor reviews on-line of many boats, and you may learn from his sardonic reviews (or not).
As always, Your Mileage May (and undoubtedly WILL vary).