Picked it up in the library, not expecting much... But, woah, within 20 seconds of reading i'm already thinking hard. This book really makes me question EVERYTHING around me, no matter which page i flick open to. The fact that each page is beautifully presented with pictures and capitilized quotes, makes it that much easier to understand. SO MUCH, in such a "small" book! I recomend it with two chin scratching thumps up!
If your looking for something a bit more dense, try Betrand Russell's A History of Western Philosophy. It is pretty in depth going from the presocratics all the way to contemporary (for Russell) analytic philosophy.