Clinton Anderson and Julie Goodnight for me! I taped all of Clintons sessions with the competition horse (a palamino rescue horse that someone could win) and I found them so useful. He pretty much shared his whole training ethos for free and while, yes, he does have fancy halters etc for sale, he makes it quite clear you can train a horse without them.
He also gets extra points from me for looking **** fine!
Julie Goodnight is also great, she covers so many different things.
There is one guy that all he seems to do is flex from side to side all episode! 'So, your horse is stiff...flex side to side!' 'Your horse needs gelding....just flex him side to side!' Gets a bit annoying! (although I have started flexing my horse, so I guess his message gets across.)