I know there is probably a thread on this somewhere. I'm currently taking lessons 2/3x a week, so I'm not looking to learn how to ride from the books, just maybe looking at having things described to me in different ways so they make sense to me when I'm on the mount.
I know a lot of people have mentions "centered riding" ((is that the name))
Centered riding can do great things for your riding, especially your seat. We have several certified instructors at our barn, including the b/o who is a level 2. Also we've done a lot of clinics over the years with level 3 and 4 instructors. Sally Swift wrote 2 books. The original is "Centered Riding" which has the basics and is a great introduction. "Centered Riding 2" is loaded with pictures and has tons of exercises, many of which I remember from the clinics I attended and my lessons. It is very classical in its approach and appropriate for all disciplines, including western. It is amazing how little changes in your body can have a profound effect on how your horses go.
I got CR on eBay, volume 2 from either overstock.com or amazon.
Hunter Seat Equitation by George H. Morris The American Jumping Style by GHM Learning to Ride, Hunt, and Show by Gordon Wright Winning..... by Anna Jane White-Mullin Judging Hunters and Hunterseat Equitation AJW-M The Complete Guide to Hunterseat Training, Showing and Judging by Anna Jane White-Mullin (basically a compilation of the two previous books) Riding Hunters,. Jumpers and Equitation by Geoff Teal 101 Jumping Excercises by Linda Allen