personally, I love using organic shampoos- they're best for the horses' skin.
What I often use is "natural instict" organic lavender shampoo, because the lavender scent keeps the flies off them a bit, specially the mozzies at night =]
It worked really well on louboyy, his tail went like silver =D it was so cool =P
I throw my heart over the fence, and he follows it. ~Sir Louie VI- my showjumper, my best friend, my everything-iloveyou.