The only Mariah Carey song I ever hear anymore is "Emotions." She had so many "soft" tracks, but they just don't fit in to what the AC format is trying to do these days, I guess. I'm looking for a day soon that even "Because You Loved Me" will be too soft for the format; Celine Dion, for the most part, has lost most AC airplay, and she was at one time a staple.
Madonna's 90s material has been pretty much forgotten, unfortunately. Her post-"Vogue" tracks have faded in to oblivion. Other than the occasional "Take A Bow" spin, the majority of her 90s music hasn't lasted.
Gloria Estefan had some awesome songs, but again, many are probably too slow for the format now. I never hear her anymore, and I think her rendition of "Turn The Beat Around" as well as "Conga" are very 2012 AC-friendly.