Sailing Fundamentals by Gary Jobson
This book is the standard basic keel boat manual for American Sailing Association (ASA) certification course.

The New Book of Sail Trim Edited by Ken Textor
Covers basics of sail trim as well as the common sails and their care and use.  Cruising spinnakers and downwind twin head sails are some of the most interesting topics.

Boat Docking - Close Quarters Maneuvering for Small Craft by Charles T. Low
Focuses on slow speed maneuvering under power with a single engine. Lots of illustrations on how to get out of the most difficult situations while docking.  Great book to have handy when you don't have a clue to get off the dock safely in adverse conditions.

Illustrated Sail and Rig Tuning by Ivar Dedekam
A poorly tuned is dangerous. Knowing how to keep the right tension on rigging will keep the mast in the boat where it should be.  A absolute must to have on every boat. 

Surveying Fiberglass Sailboats by Henry C. Mustin
If you think that you really don't need to have a survey before purchasing your next boat, read this book. After reading it and understanding the many possible problems that may be lurking under the gel coat you will change your mind and hire a reputable surveyor.

US Sailing Certification Series - Coastal Navigation 
Good basic navigation book.  More than you will ever need in this modern world of cheap mapping GPS.

The American Practical Navigator (AKA Bowditch)
This is a must have book, covers every detail of navigation, tide, weather, charts, radio wave propagation and much much more.  Get it and put it on the shelf to read when you think you know everything, it will make you remember how much more there is to know.

Marine Diesel Engines by Nigel Calder
Knowing what you can fix yourself and what needs a specialist can save your thousands in repair or replacement bills.  Cruisers should get this one, read it, and keep it on board where you can find it.

Spinnaker Handling by Bent Aarre
Demystify that spinnaker set, keep that huge sail under control and bring her down like a pro.  This book is for your racing crew.  Get them all a copy and make sure they read it.

The Practical Mariner's Book of Knowledge
This one is for the sailor who has everything.  Great gift will keep you laughing.  The last resource when you just can't find that renaming ceremony or special sea tested solution.

Annapolis Book of Seamanship by John Rousmaniere
Covers all the basics and a good general book for covering all the basics.  This is a must read for everyone. Covering the merits of the varous boat designs, how to get underway, sail trim, weather, sail handing gear and knots, personal safety, rules of the road, navigation aids, compass, position finding and  anchoring among other subjects it is a well rounded book.  You may find that the information may lack the depth of the other books listed here which focus on a single topic.

The Complete Book of Anchoring and Mooring by Earl R. Hinz
This is the anchoring bible if there is one.  Don't leave port without this one.

Championship Tactics by Gary Jobson, Tom Whidden, and Adam Loory
These guys are the best of the best and give there secrets away freely in a series of stories that both teach the concepts and entertain.  You will not be able to put this one down. 

Sailing Smart by Buddy Melges and Charles Mason
Another book by the guys who have won all the cups in the major world racing scene.  Any information they share is worth it weight.  A more methodical perspective with clear insight into what it takes to win at the international level.

ASA Cruising Fundamentals 
This is the guide to coastal cruising and bareboat chartering.  Covers the information required to operate and maintain a cruising sailboat.  Focusing on the basics like use of the head and how to start the engine.

Nigel Calder's Cruising Handbook
Cruiser's indispensable book of knowledge. 

Boatowner's Mechanical and Electrical Manual (second edition) by Nigel Calder
This book is the book to have when things go wrong. Get it before your need it.