When I was in elementary school I read every single horse book in the school library (and some non horse books as well.) I read all of the Billy and Blaze books the school had.
The Blaze books were written and illustrated beautifully by C.W. Anderson. According to Wikipedia "The adventures of Billy and Blaze revolved around proper care of the horse, while teaching a lesson. Anderson would go to great lengths to give accurate information." I have to say that I don't remember any of the stories, and now I am going to have to hunt down copies to reread, but I do remember enjoying them thoroughly.
The library also had a nearly complete (for the time) set of Walter Farley's Black Stallion series.
I remember chanting rather inanely at a girl scout meeting (I was not a big fan of girl scouts and my career there was short lived) that I wanted to go to "Arabia" so that I could get my own arabian horse like the Black. (Which I have always lamented was a sadly uncreative name for a beautiful horse.) I also remember crying during the scenes in the Black Stallion and the Girl, when one of the horses is injured in a race while Pam is riding her. Besides the Black Stallion, Walter Farley also wrote some books about Flame, the Island Stallion. I can't say I enjoyed those as much. You just couldn't get behind a rival to the Black, even when he was no longer a rival.
The first book I ever purchased with my own money (allowance saved over a couple of months) was a beautiful copy of Black Beauty by Anna Sewell. I still have it, and it remains one of my prized possessions. (Along with the signed first edition Mark Twain inherited from my great-great grandmother.) It had the prettiest painted cover, directly on the binding, with a clear dust jacket over it. It is safely stored right now and I can't access it to take a picture, and though I searched I cannot find it among the many varied cover pictures online. I did however find this: (which I also own)
My favorite thing about Black Beauty is the fact that it is written from the horse's perspective, without being cheesy or cartoonish. At the age of 8 I stayed up until 1:00 AM, reading each heartrending word of Beauty's tale, until his peaceful retirement in old age. But I still think of poor Ginger, and Merrylegs, and how their fates were effected by the whim of their owners. I woke my parents up (at 1:00 AM) to let them know of my achievement when I finished. (And probably for a little comfort before I tried to go to sleep.)
I also read all the other classic horse books, National Velvet, the Marguerite Henry books, Misty of Chincoteague and sequels (I have a copy of Misty signed by Maureen Bebe from a trip to the island on a family vacation) and Mary O'Hara's My Friend Flicka just to name a few.
By the time the Saddle Club and other chapter based horse series began to come about I was already in high school and they were a bit below my reading level, but I read them anyway. At least until about book 20. There are over 100 now, plus "Super Editions" and two spin off series. One for younger readers, Pony Tails, and one for older readers, Pine Hollow. I discovered the Pine Hollow series a few years ago and read through them in rather rapid succession and was quite depressed in the last book when Pine Hollow burned to the ground, and several of the horses died. I felt like a part of my childhood had been taken away. It seemed to me almost insulting, like she(the author) was tired of the series and wanted closure from it. Like certain musicians who "tire" of a song that made them popular and refuse to play it anymore.
However Bonnie Bryant, prolific author of the Saddle Club series, inspired many imitators, some surpassing the original in content. The Heartland series by Lauren Brooke, the Thoroughbred series by Joanna Campbell have equally lengthy bibliographies just to name a few.
Around the time that I was running out of specifically "horse books" I discovered Mercedes Lackey and the science fiction fantasy genre due to one cover picture of a glowing white horse, and my reading interests were never the same.
Anyone who has ever ridden a horse, and read this series has secretly (or not so secretly) wanted a Companion. A beautiful white horse caparisoned in blue and silver, with hoof beats like bells to come and choose them and take them away to a life of heroism. Now Ms. Lackey does a wonderful job of making heroism real. Showing how it is long stretches of the mundane, marred by intense bursts of terror and travail. Her heroes are flawed (as all good heroes are) but they have the adoration, wisdom and trust of one true Companion to bolster them throughout. Who wouldn't want that? Despite the price.
There are other series that strive to emulate this connection, and the bond between horse and hero, and they are enjoyable. But none are as engrossing as the original which defined the genre.
The Dark Horse series by Mary H. Herbert
The Green Rider series by Kristen Britain
The Mountain's Call by Caitlin Brennan
The Horse Mistress Saga by Toby Bishop
There is however a Science Fiction novel about horses that hearkens back to Black Beauty, in that it is told from the horse's point of view, all the while creating a rich and elaborate mythology that I have only found in some of the best written books. This duology written by Mary Stanton beings with The Heavenly Horse of the Outermost West. And while this excellent novel has long been out of print, any time I run across a copy at a used book store or book sale I buy it, so that I can give it to friends who have not read it. It is a dynamic novel with complex characters, intimate knowledge of equine herd behavior beautifully anthropomorphized and wrapped in an intense mythological battle between good and evil, gods and devils of the equine persuasion. The sequel, Piper at the Gate is just as enthralling.
I have tried to focus this post on the good among scores of horse books. This does not mean that there are not many many books out there that are full of poor plotting, bad dialogue, and misinformation about horses. In fact with the exception of non-fiction, which is a completely different topic, most adult novels that have horses as a main premise tend to be poorly written romance novels. I won't dwell on these overly, but there is one I have to mention.
I walked into a book store, and asked for a recommendation for a "horse book for grown ups" and this was what was recommended to me. (By someone who had hopefully never read it or they should be slapped.) Riding Lessons by Sara Gruen. The main character is one of the most ridiculous and unlikeable people I have ever read. In the first chapter she loses her job, is told by her husband that he is leaving her and has problems with her miscreant daughter (all on the same day.) In an attempt to repair her life she returns to her parents farm, and through extreme acts of ineptitude and outright lying she comes close to destroying their business and apparently steals a horse. I think the author means for us to feel sympathy for this woman, but I have no idea why we should. Suffice it to say I didn't get much further and don't know what implausible things happened to "fix" her situation, because frankly, I couldn't care. She didn't deserve a happy ending. And I rarely read for sad ones. There is also a sequel to this book that I purchased at the same time, but have never cracked the cover.
That said, I have read many more good books about horses than bad. And I am sure I am forgetting dozens of them in this post. If anyone has any favorite horse books I have left out, please feel free to comment. If I haven't read them I could definitely use a good recommendation.