PeeWee Herman's giant foil ball doesn't have anything on this.  For one thing, it's PeeWee Herman.  I mean, he's cool enough...  I don't know.  The other thing is that for play, Lego bricks beat aluminum foil hands down 6 days out of the week and twice on Sunday.  Flickr's Chasingfun proves my theory correct with a giant Lego ball.  It rolled about 15 yards down 19th Street in San Francisco before they stopped it.  Check it by clicking to enlarge...