Reference Sources on the Internet
http://www.asindexing.org/site/refbooks.shtml

American Society of Indexers

Abstract:

These are resources that professional indexers may find useful in their daily work. Please visit Yahoo's resources if you are looking for beginner's guides to the Internet, or visit the Internet Public Library for more general reference sources. If you want only thesauri, narrow your search by looking at ASI's list of online thesauri.