Rihanna is the latest artist to appear nude on a magazine cover (for GQ's December issue), but she follows dozens of other artists who've stripped down over the past 30 years. From John Lennon on the 1981 cover of Rolling Stone, to Britney and Christina showing off their pregnant stomachs for Marie Claire and Harper's Bazaar, to Billboard's own nude photoshoot with Bret Michaels, here are 25 of music's most naked magazine covers.