A short, small book illustrating philosophical principles through jokes, such as this one about relativity:
Pat: "Mike, I'm calling you from the freeway on my new cell phone."
Mike:"Be careful, Pat. They just said on the radio that there's a nut driving the wrong way on the freeway."
Pat: "One nut? Hell, there are hundreds of them!"
There's no depth, but it is pretty handy if one is looking for a quick description of, say, existentialism.
Small Favor — Jim Butcher
Dresden fights fallen angels and the billy goats gruff. Great fun, as usual.