Pinball Machine Care & Maintenance by Bernard Bear Kamoroff.
I bought this book a few years back and it's been sitting on my bookshelf waiting for its golden hour to arrive. The book covers the basics of what pinball machines are all about; all their various components as well as common problems and repairs. It gave me a great introduction and I've been looking up stuff in it contantly.
I bought it direct from the publisher, but it's also available from most suppliers (such as GameRoom Magazine ).

This Old Pinball (aka TOP) DVDs
These are excellent instructional videos presented in an entertaining and interesting manner. TOP #1 deals with shopping an older electromechanical (EM) pin, but has a lot of general resoration tips that are relevant to restoring any pin. #3 covers repairs to a Twilight Zone pin and has also been very helpful. I can't comment on any others (yet) but at $8 a pop I'm sure they're well worth picking up. The TOP website also has some free podcast videos that are aimed at the absolute beginner.
http://marvin3m.com/top

Marvin3M's Pinball Repair Website
Marvin Yagoda operates Marvin's Marvelous Mechanical Museum in Farmington Hills, MI. He's been very passionate about this hobby for almost 50 years and has compiled a plethora of detailed information that covers every conceivable aspect of pinball repair. If his site was to ever be compiled and published in printed format, it would no doubt be called 'The Pinball Bible'.
http://marvin3m.com/fix.htm

Life After Death DVDs
After reading some of Rob Craigs 'Tales of the Silverball' articles in GameRoom Magazine, I figured these would definitely be worth a look. There are 3 available and I picked up the first two. While not as exhaustive as the This Old Pinball videos, it was great to see some restoration techniques and opinions from someone else (especially since he works on some early 80's Stern pinball machines that are similar to mine).
These are also available from the GameRoom Magazine Webstore .

Other Noteable Websites and Blogs...
The Internet Pinball Machine Database - An essential resource for any pinball fan. Every pin ever made is detailed and open for review/comments. There's also a huge amount of downloadable manuals and photos and other materials.
The Internet Pinball Serial Number Database - Lets visitors submit and tracks individual pinball machines around the world and presents all that info in a variety of ways.
Ed Cheung - Ed covers his extensive work on restoring his pinball machines to their former glory.