We all know the ones almost everyone uses.. "Whoa...", "Easy..." and so on.
In my experience, I've rode better and my horses have worked better if I'm constantly talking to them or even singing... it helps me breathe, relax and therefore, it helps the horse relax and just makes the whole ride better. I know this doesn't technically count as vocal cues, but it helps SO much.
Just some random food for thought.
I'd like everyones opinions as well!