Dan Ariely really seems to have sussed things out: his rational thinking when most of us would get over excited about a deal is refreshing, and interesting. I like the way he dissects things for you, yet leaves you time to think about the deals as well. He lets you make your mind up about what you'd do, then he usually runs an experiment - then you see how you faired with other people.
Great read for anyone into marketing, psychology, human sociology and behaviours in the world. Also a good read for those of you who can be sucked in by marketing, targeted adverts and other forms of selling.