An interactive online Eugene O'Neill forum.
An incredible resource. Includes e-texts of his works, scholarly studies, online forums, and as much information on the great playwright as anyone could possibly need. Handsomely designed, too!
Lucid café's site on O'Neill.
http://www.lucidcafe.com/lucidcafe/library/95oct/egoneill.html
Includes bio and good links.
The Tao House.
http://www.eoneill.com/eof/index.htm
The Tao House, in Danville, California, was where O'Neill wrote many of his most famous plays. This site is the home of a historical foundation with more personal resources on O'Neill, including letters, photos, and information on manuscripts. Another nice site.
PBS's site connected to a production of O'Neill's most famous play.
http://www.pbs.org/wnet/gperf/longdaysjourney/
A good site, with insights on the work.
The Nobel Foundation's web entry on O'Neill.
http://www.nobel.se/literature/laureates/1936/
Includes his autobiography and audio files. Another cool resource.