Does anyone know of a good textbook with challenging problems for Intermediate E&M? The one we are using in my class is "Introduction to Electrodynamics" 3rd ed. by Griffiths. I looked at the problems in the book, and they don't seem to be hard enough. I'm not really looking for problems that are more math-intensive, but problems for which the basic concept needs to be applied to a difficult application. Does anyone have a suggestion?