Well, it depends on what you are looking for, if you want an all around knitting book you could borrow from your library (for a test run) or buy these books to name a few.
Knitter's Handbook: A Comprehensive Guide to the Principles and Techniques of Handknitting by Montse Stanley
The Knitter's Book of Finishing Techniques by Nancie M. Wiseman
Vogue Knitting: The Ultimate Knitting Book
and the ubiquitous Knitting Without Tears: Basic Techniques and Easy-to-Follow Directions for Garments to Fit All Sizes by Elizabeth Zimmerman
(I also like Jacqueline Fee's The Sweater Workshop you get to work on a little windsock type thing while learning basic fitting methods)
and in those moments of crisis it is nice to have a book or two on how to help fix mistakes (which we never make, they are learning experiences ):
The Knitting Answer Book: Solutions to Every Problem You'll Ever Face ... by Margaret Radcliffe
Knit Fix: Problem Solving for Knitters by Lisa Kartus
If you decide to buy any of these books you might want to purchase them at Amazon.com or http://www.knitpicks.com.
They tend to be cheaper than picking them up at a local B&N, Borders, etc.
By the by have you seen these two cable scarves (http://knitty.com/ISSUEwinter06/PATTelbac.html) from an older issue of Knitty. They are nice to wear since they are reversible.