[Say, it isn't that bad!]

I seem to remember some sort of fantasy series where divinely-blessed horse-shaped people chose human compatriots as champions for an isolated kingdom.

I think it had a few books.

Spoiler:  

Want a hint? It has more series than some successful writers have books.

Spoiler:  

It's called Heralds of Valdemar, it's pretty much exactly what you're talking about.

Spoiler:  

Mercedes Lackey is pretty solid writer, and unlike some, can finish writing books and series. However, there is a disturbing undertone of "yaayfriendlymindcontrol", but if you're ok with reading X-Men, you probably will be ok with reading this.