The book Classical Electrodynamics by John David Jackson (3rd ed. Wiley) is one of the few true classics of theoretical physics, no matter what field you specialize in. And the problems in the book are interesting, but often quite difficult.
There are many people posting solutions to subsets of this book online - I only think mine are better, because I believe them to be correct. I hope they can prove useful to someone else, that's why I have compiled them into a solutions compendium.