Bad Science by Ben Goldacre. This is a fantastic, but scary book. If any other subject was reported as inaccurately or irresponsibly as science is there'd be outcry, but because we're so ready to believe the latest fads and scares we (at best) waste fortunes buying useless things, or (at worst) die!
If you don't understand science read this book - it's written for you. If you do understand science read this book - you'll be amazed at what goes on.
If you want to get a taster of Ben's work before buying the book - he writes a column for the Guardian newspaper.