I bought a book called "The Yorkshire Terrier" by Deborah Wood. I've found it to be very informative and interesting, even goes back through the history of the yorkie. It has lots of good training tips which I've tried, and they have worked really well. It also comes with a training DVD, but I haven't looked at that yet. Just thought I'd let everyone know in case you're looking for a good yorkie book. I've ordered "Yorkshire Terriers for Dummies" and should get that one this week.
Here's a link where you can read about the book.
http://www.powells.com/biblio?isbn=0793836441