A good introduction to stellar spectroscopy appeared in the October 1996 issue of Sky & Telescope magazine on pages 48-51. The article includes an excellent set of reference spectra. A version of this article can be seen at http://www.skyandtelescope.com/howto/basics/3305876.html. Also see the September 2000 issue, pages 38-44 and the August 2004 issue, pages 44-49.

The best book on this subject is "Stars and Their Spectra" by James B. Kaler, Cambridge University Press. It is available through Willman-Bell, Inc. See Willman-Bell's monthly ad in Sky & Telescope or go to www.willbell.com.

The Peterson Field Guides, "Stars and Planets", Fourth Edition, by Jay M. Pasachoff, contains a set of star maps that are useful with a spectroscope. Stars to sixth magnitude are color coded according to spectral type.

"A Spectroscopic Atlas of Bright Stars", A Pocket Field Guide, by Jack Martin.
Published by www.springer.com.