While working on the cookbook, I came across some really great books that I highly recommend to fans of Mathematics:
Generatingfunctionology by Herbert S. Wilf. This book begins with an awesome quote, "A generating function is a clothesline on which we hang up a sequence of numbers for display."
Fundamental Finite Element Analysis and Applications with Mathematica and Matlab Computations by M. Asghar Bhatti. This book really helped me wrap my mind around the ideas of FEM. Expensive book, but worth it.
A Student's Guide to Maxwell's Equations by Dan Fleisch is really helpful in taking the mystery out of these equations. It decomposes them symbol by symbol in a way I never seen done before in a mathematics or physics text.
There are a few others but I'll save them for a future post.