THE FACH SYSTEM
Handbuch der Oper (out of print)
Amazon.com will do a search for you and find a used one, if available.
By Rudolf Kloiber and Wulf Konold
Publisher: DTV
ISBN: 3-423-03297-9
OR
Publisher: Bärenreiter
ISBN: 3-7618-3297-9
www.baerenreiter.com
Cantabile-Subito
Great site with fach lists (according to Kloiber), repertoire lists, descriptions of voice types, discussions of great singers of the past, recordings, books, conductors, wonderful photos, and many other goodies.
http://www.cantabile-subito.de/Categories/categories.html
For more information:
Karen Mercedes' lists of suggested repertoire for all voice types:
www.radix.net/~dalila/rep.html