I loved Nico the Unicorn, What can I say? -- Watch Nico the Unicorn Online Free Putlocker | Putlocker - Watch Movies Online Free
The Red Pony (1973) is based on the book (can't say how accurately) and I really enjoyed it. It's not your typical "damaged teenage girl meets horse nobody wants and together they defy all odds" horse movie.
Touching Wild Horses (2002). It's not focused entirely on the horses, but it's a very nice story in my opinion.
I vote we all band together and start our own realistic horse movie corporation. We will not have any of those inaccuracies that we horse people notice (constant neighing, talking animals, hopping on a horse and yelling "HeYAHH!" while slapping the reins every which way). We can also have actors/actresses that can actually ride (not to say none of the actors in the movies can ride, but I'm sure you've seen some of the people).