The Ralph Files - Voices
Alphabetical listing of character names with the actors who voice them.
The Simpsons Archive
Detailed guide with character lists, voice credits, and celebrity appearances.
The Simpsons Fans at About.com
List of links to cast information, articles and interviews.
The Voice Actor Page
Over 200 credits as contributed by viewers.
Voice Chasers
Cast list with links to the actors' pages.