I use the Large Dog version of the furminator because it does a good job of digging up the clumpy dander after they've been in the rain.
A hard bristled plastic brush so I can easily wash them (each horse has their own).
Last but certainly not least, the Shop Vac. I have one horse that thinks he's at the day spa when I get the vacuum out. He loves loves loves his face massaged
A good trick for brushing the face is to either buy those cotton garden gloves with the nubbies on them or buy the dog grooming mitts at WalMart with the nubbies on them.
You can just hug on your horse's face and massage the insides of their ears without them realizing that you're densitizing them to having something in their ears