Previous discussion on HN: http://news.ycombinator.com/item?id=376631

Some other interesting explanations:

http://yudkowsky.net/rational/technical

http://wiki.lesswrong.com/wiki/Bayes%27_theorem

http://lesswrong.com/lw/2b0/bayes_theorem_illustrated_my_way

http://commonsenseatheism.com/?p=13156