Wow, great thread, awesome tips!
I don't have anything to add, really. I guess I'll just say something most of you are probably already doing: I'm really careful to always brush, or even sponge if needed, the bridle marks off Arrow's face, over his forehead, and around his ears after a ride. It makes them so much more comfortable! Arrow's always good about it, but yesterday it was 70 degrees in Ohio, and he has a full winter coat almost! When I brought out the water and the sponge, he dropped his head almost to the ground for the first time ever and closed his eyes and waited--he was just begging me to sponge all that sticky sweat away!