Problem Solving Techniques
People often talk about the importance of problem solving skills, but there's shockingly few resources that analyze the problem solving process from a general point of view (outside of some problem solving domain).  Does anyone have any non-orthodox suggestions for books/essays on problem solving?Polya's "How to Solve It" and Paul Zeitz's "Art and Craft of Problem Solving" are both great.  Are there other resources on this topic that are worth reading?