Normally my horse doesn't get any supplements by right now he's getting:
Cough Free (because he's been coughing a little during our rides)
Gelatin (got the idea from this forum; I had a box that just expired in my cupboard, so I figured I'd give it to him for a couple months and see if I could tell any difference)
I help with the feeding at my barn every once in a while and some of the horses are on a TON of supplements. The ones I can remember are noni, MSM, glucosamine, wormer, sunflower seeds, Vit B, baking soda, cayenne pepper, silver water, thryoid (not sure what it's actually called), bio-meth, and anti-hist, mare magic, and calm & cool.