Getting Started in Electronics, by Forrest Mims is a classic. It covers the real basic stuff, and while you don't need
to understand any of it to do a decent bending job it certainly helps an awful lot to have a general idea about what's going on.
Electronic Projects for Musicians, by Craig Anderton also has an excellent explanation of basic electronic principles, which I found to be slightly more user-friendly that the Forrest Mims stuff, but not quite as detailed.
For bending information, the Reed Ghazala book is much better than I had expected.
