Christopher Hitchens, Richard Dawkins, Salman Rushdie, Lawrence Krauss and Bill Maher have all slammed Islam very very hard. I can't think of as many prominent Christian leaders that have been as brutally critical of Islam as they have. Franklin Graham comes to mind. But his comments are rather banal in comparison.
Ayaan Hirsi Ali is an atheist. Although given her early upbringing as a Muslim, undergoing female mutilation at 5 years old, one can understand why.