natural horsemanship videos in general are really good, because they work with the mentality of the horse.
Also, you can get a big binder with lots of papers in it, called "John Lyons' conditioned response Training mannual- GROUND CONTROL (teaching manual for unbroke and broke horses)" yes I realise that is a huge title, im sorry I just quoted everything it said on the front =P
Anyways, that's a great lot of stuff there. Personally I havent read much from it, but my mum went to a workshop with her horse and they went through a fair bit of that and it helped her heaps, and she taught me some things from that. Theres spaces for you to take notes on how your horse did everytime too, so you can keep track of what you need to work on. Or if you have more than one horse, where you're up to with each.
The books is great. Lots of pictures and diagrams too.
There is also a DVD by the Australian Natural Horsemanship Study Centre called "Ken Faulkner- Secondary groundskills" (this is the one that's here with me now, but im assuming theres a "primary groundskills" one too, and we have another one [which is probably the primary one]). Anyways, that's a pretty good dvd too.
Hope it helped
I throw my heart over the fence, and he follows it. ~Sir Louie VI- my showjumper, my best friend, my everything-iloveyou.