sentence: the tribute concert , which took place at wembley stadium for an audience of 72,000 , featured a wide variety of guests including ; robert plant ( of led zeppelin ) , roger daltrey ( of the who ) , extreme , elton john , metallica , david bowie , annie lennox , tony iommi ( of black sabbath ) , guns n ' roses , elizabeth taylor , george michael , def leppard , seal and liza minnelli .