It has been mentioned by a few already but Matt Hampson has got to be next on your list. I read it when I was 17 and was like wow this is good. I gave it to my dad recently who will happily admit he doesn't know one end of a rugby ball to another but he read this book in a weekend and was like "that is the best biography I have read".
O'Connell's is a nice read and has a good pace but you have got to get the Hampson one.