Guys, what's the sexiest thing a girl can wear?

Nothing at all ;o (kidding). Like others have said before, it depends on the guy. Hair up or hair down depending on the mood, though more than often I would say hair down and loose/wild. Clothes that aren't real revealing, but aren't real conservative either. Skirts (not too long- you aren't a libraian are you? not too short- don't want us to think you came straight from Vegas). Tighter shirts are definitely more "appealing" but again, nothing real revealing. Somewhere in the middle.

Really depends on the guy. There isn't one thing every girl can wear that is gonna be the best for every guy. It also depends on the circumstance as well. If its a date a long skirt, tight top and her hair down. If alone I prefer a shorter skirt. Really just depends. If she looks attractive in an outfit she knows it and it works together.