So far, my favorite is Masters: Gemstones: Major Works by Leading Jewelers (Masters). Wow! While some of the work isn't to my taste (hardly a surprise- there's a huge range of styles represented), it's all beautifully made and nicely photographed. Several artists have spurred ideas that I can apply to my work- as well as giving me somethng to aspire to in terms of sheer gorgeousness! So: highly recommended.
I will probably post more about other books soon. Meanwhile, when I find a metals resource I really like (books and DVDs, anyway), I add it to my aStore, generally with notes.