I'm so surprised Fabrice Bellard is so far down. The guy is absolutely one of the greatest developers I've ever ever had the luxury of reviewing the code of.

By comparison, DJB is a force of nature when it comes to programming, but reading his code can be a little difficult (try understanding qmail's source base as an example). I have to admit though, _why's is the most readable of all truly great code, despite the fact that it's at least mostly in ruby.