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?<p>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?