General Marketing books:

• The 22 Immutable Rules Of Marketing
• The Irresistible Offer

Books on marketing YOURSELF & Your services:

• You, INC.
• What Clients Love
• Selling The Invisible
• Make It Happen Before Lunch

While not marketing specific, I do want to highly recommend the following:

• The Millionaire Next Door
• The Millionaire Mind
• How To Think Like A CEO
• The Politics Of Life
• E-Myth Mastery
• The 7 Habits Of Highly Effective People
• Swim With The Sharks Without Being Eaten Alive
• Pushing The Envelope All The Way To The Top
• Beware The Naked Man Who Offers You His Shirt
• Dig Your Well Before You're Thirsty

Happy hunting!