Here are some other places of note on the Internet for fans of Gladys Mitchell and Golden Age mysteries:
ASH RARE BOOKS - Owner and collector Laurence Worms has a great searchable site of out-of-print and impossible-to-find books; highly recommended if you're looking for that elusive mystery title!
CRIPPEN & LANDRU PUBLISHING - Doug Greene's great publishing company provides an online catalog of their obscure crime and mystery fiction titles and collections.
TRACE EVIDENCE - Alfred Hitchcock's Mystery Magazine editor Linda Landrigan offers a great site for mystery fans that looks at short stories, the mystery genre, and the craft of writing.
HOUSE OF STRATUS PUBLISHING - Another interesting publisher who has brought back into print some long-forgotten crime fiction.
FACSIMILE DUST JACKETS - Mark Terry's great site sells quality dust jacket reproductions from classic Gladys Mitchell and other Golden Age mystery books.
THE MYSTERY PLACE - The site to preview and learn more about the stories found in Alfred Hitchcock's Mystery Magazine and Ellery Queen's Mystery Magazine, two classic publications that are still bringing crime and suspense stories to readers.
CRIMESQUAD.COM - Chris Simmons's smart contemporary crime fiction site; Miss Mitchell is featured as October 2005's Classic Crime author.
JASONHALF.COM - My personal website has information and original writing from me, and the blog is filled with summaries and reviews of classic mystery novels from various authors.
I'll add more links as I go. If you have any suggestions, please e-mail me!