The Whup-A-Bug spray that kitten posted works awesome! The best of any fly spray I've used. Endure is next in line to that.
I put fly masks on my horses and spray them down. Keeps the flies off pretty good.
SR, I think I saw something at TSC that you stick in old milk jugs to trap the flies. I think I'm going to have to try it out or rig something like it up on my own.