The following list represents some resources I've found useful in my consulting. Also, make sure you check out the Consulting Tools on the CD-ROM that accompanies this book.
Flawless Consulting by Peter Block
This is a veritable classic in the field of management consulting. However, much of the information is great for the technical consultant, tooin particular, Block's understanding of what makes a consultant and his discussions on the client/consultant relationship.
The Business of Consulting: The Basics and Beyond by Elaine Beich
This book covers the nuts and bolts of many of the business aspects of consulting. From determining your rate to marketing tips, correspondence, contracts, and negotiations, Beich does an excellent job of providing tangible and pragmatic information.
Dangerous Company: The Consulting Powerhouses and the Businesses They Save and Ruin by Charles Madigan and James O'Shea
This book was written as an exposé on management consulting, covering some interesting history of the field. Its message is extremely effective in driving home the idea that advice has value only if it is valuable. If consulting is to be your future, you would do well to understand and heed that message.
The Entrepreneur Magazine Small Business Advisor by Entrepreneur Media
This tome is packed with nuts and bolts on starting, developing, and running a small business. From discussing business plans to financial analysis and selling your business, this book is extremely concise and well organized. If you're serious about your business, you'll refer to this book often.
The Goal by Eliyahu Goldratt
This is a classic in business literature. It was and might still be required reading in Pepperdine University's MBA program. Written as a novel, this book covers the restructuring of a manufacturing company. As the story develops, you discover, with the protagonist, much of what doesn't work and some of the most useful ideas in business.