Get the "Art of Rigging" series by Kiaran Ritchie. There's 3 in the series and I really recommend getting them all, but if yer low on cash, just get Volume 01 first. It's so far the most comprehensive book on rigging that I have seen so far. The technique and process is a little old but it's a solid book.
If you are going to buy 'Art of Rigging' I definitely suggest buying it from CG toolkit! Its e-books (I Guess thats up to preference if you'd rather want it on paper) but the main argument is that its whole lot cheaper!
Replies
[ame]http://www.amazon.com/Art-Rigging-DVD-Definitive-Character/dp/0976800314/ref=sr_1_3?s=books&ie=UTF8&qid=1297786992&sr=1-3[/ame]