Very good book on the alternatives to "positive thinking". Burkeman does a great job of taking you through all the philosophies and methods that contradict the mainstream power-of-positive-thinking self-help books.
It hits stoicism, zen, mindfulness, the problems with goals, and a great chapter on death contemplation.
If you're slightly interested in this topic, you've probably already read deeper stuff on most/all of these but Burkeman's book does a good job at looking at the landscape as a whole. Plus, he comes from a seemingly sincere joe-everybody perspective so his skepticism is always evident and refreshing.