For an anniversary present this year, my wife bought me a terrific book entitled The Principles of Knitting. It is full of really basic things in knitting and it take you through many, many neat techniques to enhance your knitting. It's really huge, weighs a ton, and it a great deal to digest. It will make a really good reference book, once I get through it.
Here is a link to the book and you can look inside it. It sells for $45, but it's usually on sale at Amazon for about $25 or so.