I've decided what I'm going to spend my Amazon voucher on. Focal press recently published a new book "Speedlights and Speedlites"
Written by a trio of Bostonian photographers Lou Jones, Bob Keenan and Steve Ostrowski,the book is all about small off camera flash and it looks kind of interesting. By the sounds of it its going to have some proprietary information about Canon and Nikon flash and promises to have diagrams. You can download a few sample pages from the focal press website for a little preview