How to Think Straight About Psychology is the best introduction to the ideas of science that I've read. It's by Keith Stanovich, the cognitive scientist who wrote Lukeprog's favourite book on the cognitive science of rationality and who is also on the board of advisors at CFAR. It introduces, amongst other things, important ideas of how science works, how pseudoscience works, two chapters on probabilistic reasoning and recommends reading Kahneman, and also a section on why we shouldn't be arguing about the meaning of words, only the differences that exist in the real world (y'know, anticipated experiences that let us test hypothesise). It also destroys a lot of public misconceptions about science and psychology.

I plan to give it to all of my friends who need a simple introduction to science. Contact me about a pdf.

Edit: By the way, for a typical LWer though, it would be very basic; sorta like one of the best books of 'Traditional Rationality' or something.