Once Aerosmith frontman Steven Tyler announced he was leaving "American Idol," you knew it would be just a matter of time before speculation about a replacement judge started up.  And according to People.com, superstar R&B songstress Mariah Carey is the producers' first choice, with the two sides already engaging in "serious talks."  Of course, it is still possible that the show may have to replace more than one judge, as Jennifer Lopez is still negotiating her contract and is undecided on whether she will return.