There's Kylie, Madonna (or Madge if you're British), and Beyonce. All people who only need one name to be identified in a conversation. Bono and Edge too I suppose. Anyone else?
If you're geeky / online most of the time, does Xeni count?
There's a sizeable number of people from my uni days who still have absolutely no idea what my real name is. There'd be more if it wasn't for that damn Royal Mail... Wait, does that mean I have to be a dictator?
In religious (monotheism/polytheism) text have one name characters: Bast, Zeus, Yahweh, God, Lucifer, Satan, Athena, Diana, Adam & Eve, Mohammad, Mars, Ares, Venus, Nike, Bacchus, Apollo, Anubis....etc