http://www.shelyak.com/en/links.html
Olivier has prepared quite a comprehensive list of books on spectroscopy.
The latest addition to my library " Stellar Spectral Classification" by Gray&Corbally is a bit heavy, but has to be the ideal "reference" work on stars.
Kitchins "Astrophysical Techniques" especially Chapter 4 on spectroscopes (BTW Chapter 3 is all about Photometry) is a worthy addition.