Outside of the coaches, instructors, masters, and grandmasters under whom I've studied, 2 books and one website helped form my core attitude towards fitness and exercise.
What is my core attitude?
Functionality - The exercise must contribute to more efficient transference of energy.
Proportion - Muscles must maintain proportion to effect an efficient transference of energy.
1. "Arnold's Bodybuilding for Men" by Arnold Schwarzenegger with Bill Dobbins
This book lays out the basics in a clear and easy-to-understand manner. Excellent for beginners as it outlines a progressive exercise routine that can be done without the need for expensive equipment. Don't let the title fool you. While the author does touch on bodybuilding in later chapters, the exercises and methods are transferable to most fitness goals. It's money well spent to get started, and a go-to resource as you grow.
2. "The Art of Expressing the Human Body" by Bruce Lee and John Little
The most comprehensive resource that chronicles Bruce Lee's complete journey to generate functional strength for his performance as a martial artist. This book covers everything from weight training to cardiovascular endurance, circuit training to stretching, nutrition, philosophy, etc... There is something for everyone here, and a great inspiration for those of us who aren't genetically gifted with a giant frame!
3. Steve Reeves International Society (http://www.stevereeves.com/)
Steve Reeves, Mr. Universe 1950, was a pioneer not only in Bodybuilding, but fitness as well. His accolades came at a time when muscle definition, proportion, and function were valued over sheer size. In his day, 'musclemen' valued both strength and endurance of the total body. Many of his training methods and nutrition ideas have remained key elements of athletic training to this day. Check out his ideas on Power Walking. This website provides a wealth of information for those who look to build functional muscle and maintaining an active lifestyle.