What are the behavioral characteristics of different breeds of horses? Arabians? Morgans? Thoroughbreds?

There is a great deal of variability in the behavior of horses, even within breeds. Some larger breeds ie. Shires, Irish Drafts etc are categorized as gentle giants, whereas Thoroughbreds and Arabs are renown for being slightly skittish and forward going. However there are always exceptions to the rules. Environmental factors makes a huge impact on the behavior of a horse, and can cause them to display hugely unexpected traits. For generalized traits of certain breeds you can indeed use a book or a website like the one below, which will probably tell you what to expect from certain breeds, behavior wise. It should tell you whether the breed is known to be placid or temperamental, however you may come across a horse that is described in the book as highly strung, but in real life is a placid and laid back horse.