About.com  Mystery Authors Directory, reviews, etc.
Authors on the Web  Information on Authors and their latest projects
Black Raven Press  Publishers of Mystery News
Book Browser Reviews  Oodles of book reviews
Cluelass  Home of the Deadly Directory resource for booksellers, conventions, awards
Crime.com  Crime statistics, author interviews and other crime related info
Deadly Pleasures Magazine  Mystery fan magazine, reviews, articles, convention info.
DorothyL  Offical DorothyL website
Grobius Shortling Mystery Home Page  A mystery resource
Gumshoe Site  A fun site for mystery fans
I Love a Mystery Newsletter  A newsletter filled with oodles of mystery reviews
January Magazine  Online book reviews and author interviews
Mysteries in Print  Lists new and upcoming books
Mysterical-E  Mystery E-zine, reviews, interviews and lots more
Mystery Guide  Reviews of mysteries and thrillers
MysteryNet  the Online Mystery Network
Mystery News  Reviews and author interviews
Over My Dead Body!  The mystery magazine online
Page One Literary Newsletter  A site about writers for writers
Rebecca Reads.com  Great books, reviews & eInterviews
Stop You're Killing Me  Resource guide for mystery lovers
Ultimate Mystery/Detective Website Internet mystery guide 

Alibris  Online book search engine
American Book Exchange  Network of independent booksellers
Bookfinder  Booksellers search engine, good for first editions and rare books
BookSense  Independent booksellers
BookWeb  The American Booksellers Association's site.
IMBA  The Independent Mystery Booksellers Association
Tomfolio  International co-op of used and rare independent booksellers

Thanks to Barbara Seranella and her webmaster Jamie Wallace of Wallace Webs for letting us incorporate their list of mystery related sites.