Sharapova was the last in 2012, and it's surprising, given her limited game.
Out of current slam winners, the obvious candidates (in order of probability) would be Azarenka (hit at least the semis of each slam), Kvitova (her big game can pay off on any surface), and Li Na (QF at Wimbledon, semis or better at all the other slams).
Azarenka has problems getting past Serena. Kvitova has mental issues. Li Na has some mental issues combined with getting old. I suppose that Kuznetsova is a possibility, but she lacks consistency and makes Kvitova look like a pillar of mental strength.