This is COOL*: www.literature-map.com
Here's how it works: type in an author that you're fond of: J.R.R. Tolkien, C.S. Lewis, Agatha Christie, Sir Arthur Conan Doyle, Robin McKinley, J.K. Rowling (all favorites of mine), whoever. Literature Map brings up a cloud around the author of other authors people are likely to enjoy if they enjoy the work of the person they typed in. The closer two names are to each other, the more likely you are to like one if you like the other. Make sense? And it actually works! I put in Tolkien. When it brought up the cloud, not only had I read a lot of the other authors, but they're very well related, and I like them (LOTS). If you're looking for something to read (Cara), this will definitely help. Andrea, what do you think? (Hat-tip: Jonah).
Other cool internet discovery: Lists of Bests. Credit to Cara on this one. Lists of Pulitzer winners, Caldecotts, and other categories. Just cool stuff! Especially for someone whose library is running thin on books she hasn't read a gazillion times:).
*How much of a nerd does it make me that I think this is one of the coolest things I've seen online in eons?
Footnote (for Harry Potter fans only): read this editorial. It'll take you forever, but it's interesting if you can survive the white-on-black font. And it's the only thing that's ever made me think that maybe, just maybe, Snape isn't, or at least wasn't, evil. Discuss!