The Black Eyed Peas announced Thursday that they are withdrawing from this week's "Michael Forever" concert honoring the late pop legend Michael Jackson.  The band didn't elaborate any more than to say it was withdrawing due to "unavoidable circumstances."  The concert, taking place Saturday at the Millennium Stadium in Cardiff, Wales, will still have plenty of big names, however, as Christina Aguilera, Smokey Robinson, Gladys Knight, Leona Lewis and Gnarls Barkley's Cee Lo Green are still scheduled to perform.