The Ultimate Resource Book by Russell Cook
This is the just the most comprehensive book for the beginner/intermediate player! It has charts that will help you find any chord or scale on the hammered duclimer. Cool! I kept this one close at hand when I was in the early stages and it is a terrific tool for learning the layout of the hammer dulcimer and is one that I use for referencing when I'm teaching students. You will love having this big, fat book on your side, helping you learn your way around your beautiful HD. An excellent resource with over 300 pages!