Nick Bostrom has posted a PDF of his Anthropic Bias book: http://www.anthropic-principle.com/book/anthropicbias.html

As someone who read it years ago when you had to ILL or buy it, I'm very pleased to see it up and heartily recommend it to everyone on LW who hasn't read it yet. (If you don't want to follow the link and see for yourself, the book focuses on the Doomsday problem and some related issues like Sleeping Beauty, which, incidentally, has come up here recently.)