Alpheus Williams' is most impressive for its outlandishness, but I'd have to go with Ambrose Burnside's famous facial hair. He just carries it off with so much pizzazz, and I frickin' love that hat:
He strikes me as the kind of guy you'd want to hang out with and have a beer. He wasn't a stellar commander, but he was aware of his unsuitability for army command, and I admire that.
My wife is rolling her eyes at me as we speak. She's grudgingly come to accept my pirate/viking/wizard beard, but has threatened to leave me if I grow muttonchops or a giant handlebar