A brilliant resource for the study of Wolfe, with many articles on his work.
A wiki with lots of insightful information on Wolfe's work.
URTH mailing list
A long-running Wolfe-focused email discussion group, with open online archives.
The publishers of Michael Andre-Driussi's fantastic Book of the New Sun reference work, Lexicon Urthus.
Gene Wolfe on ISFDB
Quite a comprehensive bibliography of Wolfe's work
The Silk & Horn Heresy
Daniel Otto Jack Petersen's Wolfe-focused blog.
Hoof & Hide
Another blog about Wolfe and his work. The author also has a great Flickr account of Wolfe's various book covers.
"How to Read Gene Wolfe" by Neil Gaiman
"Gene Wolfe: The Man and His Work" by Michael Andre-Driussi
"The Wolf in the Labyrinth" by Michael Swanwick
"Five Steps towards Briah: Gene Wolfe’s The Book of the Long Sun" and "The Reader as Augur: Beginnings and Endings in Gene Wolfe’s The Book of the Long Sun" by Nick Gevers
Miscellaneous Science Fiction and Fantasy
The Encyclopedia of Science Fiction (Third Edition)
Fantastic resource for anyone interested in sf.
The Science Fiction and Fantasy Research Database
A very useful database of sf/f-related academic publications. Provided by Texas A&M University.