I've not had much experience in the costumes department, but the thing that I enjoy seeing men wear, especially Dominant men, would be suits. Three piece suits, ties, etc. Nothing sexier to me than a man who dresses for business. This one time(at band camp(Not really)) my Dom at the time wore a full business suit, and had me wear whatever I wanted, so I picked a tight t-shirt, and jeans. He attached a leash to my collar, and walked me around like that for hours. I could barely stand it. Not really a physical thing, it's more of a mental turn on.

Seeing Doms in cow skin, barely covering anything at all, with straps in places that shouldn't have straps, doesn't do it for me. Dress up nicely, and wooow...