I am personally a supporter of the Vetrolin line of groom products. The Vetrolin Shine spray is good for everyday or even shows and it contains natural herbs. I usually use it once every week or so, and then for Show events I use the Vetrolin shampoo, which is the best shampoo i've ever used if you want a clean-feeling, healthy looking shiney coat, then on the next morning or while i'm tacking up for the show classes I mist my horse with the Vetrolin Shine, brush it in and i'm ready to go.
Also, the silverado shine stuff works great, but it leaves streeks on certain horses. It didn't leave streaks on my horse but it left streaks on my freinds horse who is a slightly lighter shade of chestnut than mine, but she held the can too close to the horse when she sprayed it & I think that's what caused the streeks.