For a girl I'm not much of a horse person, and didn't tend to read horse books unless they had something to do with racing. Some of the ones I remember being fairly awesome were Gaudenzia by Marguerite Henry, King of the Wind by the same, and Man O' War by somebody else. (I'm just a goldmine of information, I know) Man O' War was totally the best one, and in fact remains one of my favorite books period, aside from the horse category.
It probably results from my love of spectacular sports stories, and Man O' War's record (21 starts, 20 wins) and fabulous name made a definite imprint on my memory. The other horse I remember kind of growing up with (stories of him, I never saw him race) was Secretariat. I used to love hearing the story of his winning of the Triple Crown and especially the famous Belmont Stakes race. Which was why I was so excited to find this. I finally got to see it! (Ah, I love YouTube) And then this was pretty awesome too, considering that those are just about the only horses I really was at all attached to. (You just have to ignore the appalling spelling in that one).
So that's about as far as me and horses go, but I do think that those guys were way cool.