I discovered a great website on the weekend: www.librarything.com.
This site allows you to catalogue your books (fiction and nonfiction), and you can add your own scans of the covers or choose from the covers other users have already uploaded. If you're cataloguing less than 200 books you can use the site for free; over 200 and you pay a small lifetime fee.
Once your books have been catalogued, you're able to see which other users have the same books as you in their "libraries", and new authors which suit your particular tastes are recommended. There are also dozens of book-related chat groups, discussing anything from William Burroughs to Jackie Collins to Agatha Christie.
I now have a long list of interesting-sounding mystery authors to check out: Margaret Erskine, Celia Fremlin, Shirley Jackson, Marie Belloc Lowndes, Joyce Christmas, S. S. Van Dine, Michael Gilbert... and then there's the long list of crime and mystery fiction reference books. A Reader's Guide to Classic British Mystery by Susan Oleksiw is now top of my Wants list!