In response to the e-mail asking for horse documentaries, I've liked -
PBS Nature has the Cloud series of episodes on Cloud and the mustangs.
Also, there was a Nature episode on the partnership between horse and rider (fittingly called Horse and Rider). I LOVED this one, profiled a Cow Horse champion, a polo player and a dressage instructor. Really cool.
Information on these can be found on the Nature website.
My dream documentary - one following Tevis and the riders, although I know would be a logistic nightmare. I've heard of other countries having some (Japan?) but haven't heard of a US one yet...?? Anyone? Until then, I will continue to enjoy the phenomenal webcasts that the volunteers work so hard on.