September is a big month for magazines. 562 pages of Elle! 726 pages of Vogue! Plus a hefty Vanity Fair, Manhattan, Pop ... the list goes on. We combed them all for the finest of this month's celebrity portraits, from a dangerous-looking Blake Lively in Interview to a resigned Sylvester Stallone in GQ. And just in case you haven't had enough of her lately, Britney Spears is in there, too.