Growing a Business by Paul Hawken. Treats the business as an organic enterprise. Written from the point of view that being a good human being is good for business. If everyone ran their business like this, what a great world it would be!
Small Time Operator* : How to Start Your Own Small Business, Keep Your Books, Pay Your Taxes and Stay Out of Trouble! by Bernard B. Kamoroff. Sensible advice, such that I've given copies to several friends. Reading it is like a visit with your friendly accountant uncle.

*This book is no longer in amazon.com's catalog, so the link will take you to Powell's in Portland OR. 
'I Can See You Naked' : A New Revised Edition of the National Bestseller on Making Fearless Presentations by Ron Hoff, Barrie Maguire. How to overcome your fear and the audience's boredom; how to deal with questions; getting the audience involved. Great graphics, amusing yet thorough text.
What to Ask When You Don't Know What to Say by Sam Deep, Lyle Sussman. You'll never be at a loss for words if you follow this book's principle: Stop looking for what to say, and start looking for what to ask. Goes beyond the consulting arena to touch on most of life's situations.

Secrets of Consulting by Gerald M Weinberg. Subtitled "A Guide to Giving and Getting Advice Successfully". I try to re-read this book about once a year, as a reminder to myself about what I might be missing. If you're thinking of going into the consulting business, the chapter "Putting A Price On Your Head" will be useful.