In addition to wearing All The Gear, All The Time, I'm always looking for new tips and tricks to help me keep my motorcycle upright. Lee Parks' Total Control: High Performance Street Riding Techniques is a wonderful addition to my library.
Clear illustrations, diagrams and photos paired with Parks not taking himself very seriously make for one great book.
Parks is a very accomplished rider, racer and instructor, he uses that experience to explain a lot of important ideas about HOW the bike works that I had not considered. There is a great chapter on suspension, describing how all the components work to stabilize a motorcycle and how to adjust yours for more comfortable riding. Similar chapters on traction, braking and steering pointed out things I'd love to say were obvious to me, but were not.
In the vein of Proficient Motorcycling, but more focused on physics and technology than street riding scenarios, I highly recommend Total Control.