After leaving, I still couldn't wrap my head around evolution (after the years of seing "intelligent design" in everything around me).
There's a series of videos that give a good intro to evolution and critical thinking. They've probably been posted here before, but, for any new members, these are worth watching.
Evolution: http://www.youtube.com/watch?v=XdddbYILel0
Critical thinking: http://www.youtube.com/watch?v=6OLPL5p0fMg