If you can find it, pick up Practical Horseman's Book of Riding, Training and Showing Hunters and Jumpers. It has been out of print for some time, but it's a fabulous resource. I also like the Practical Horseman's Book of Horsekeeping. Another favorite of mine is The Horse Doctor is In: A Kentucky Veterinarian's Guide to Horse Health.
-Steinkraus' "Reflections on Riding and Jumping"
-DeNemethy's book, which has some great grid exercises in the back in addition to the wealth of other information
-Littauer's "Development of Modern Riding"
While I'm not quite through all of it yet, I've been enjoying Paul Cronin's Schooling The Hunter and Sport Horse.
Littauer's "Commonsense Horsemanship" and Gordon Wright's "Learning to Ride, Hunt, and Show" are two technical ones from the Old Cavalry Guys. "In Service to Horses", (author slips my mind)is good for the inspirational side, as is Scanlan's "The Horse That God Built", about Eddie Sweat, Secretariat's groom.
I hope you manage to find all the titles you lost-good luck.