Dawkins, Dennett, Hitchens and Harris. Known as the Four Horsemen of the Apocalypse, they've between them attacked religion, religious apologetics and religious accommodationism and promoted atheism in varied and high profile ways. All four are usually very much detested by the typical religious apologist.
First found out about them by finding a talk involving Dawkins they took part in. Thought Hitchens was an annoying up-himself ponce, Harris was a pointless american bore, Dennett was a bit of a doddery guy who had difficulty getting a word in and Dawkins didn't say enough. Since then my opinion on Hitchens hasn't changed much but I find his opinions always persuasive and his frankness is welcome. Dennett is an absolute legend! Harris is cleverer than he seemed but I still find him to be a bit vacuous and boring. His opinions on spirituality and sympathy with mysticism annoys me.