The Art of Insight in Science and Engineering
I've read various drafts of this book and it really is fantastic. Rather than just teaching limited domain knowledge in science and engineering, it teaches a way to tackle ill-specified problems and how to wrestle out answers to hard questions.For the more mathematically inclined there's also a similar previous book by the same author, also available for free as a pdf:
http://mitpress.mit.edu/books/street-fighting-mathematics