Appeal is the word librarians and other reading mavens use to describe what it is about a particular book that makes it work for a particular reader. If you often enjoy fast-paced (or leisurely-told) stories, complex (or archetypal) characters, lush (or straightforward) descriptions, and cosy (or exotic) settings, you have some clear preferences that can help you find books that will suit your tastes.
The sites we link to in the middle box on this page are experiments in using those sorts of preferences, and some adventurous coding, to automatically generate book suggestions. They're not always particularly reliable, but they can be a lot of fun!
Gnooks - "Take a ride" on Gnod by telling it three of your favorite authors, and check out literature maps to see which authors resemble each other.
What Should I Read Next - The minimalist's favorite: Tell it one book you've liked, and it will search its users' booklists to suggest others you might enjoy.
Whichbook - Sliders (for variables like "happy/sad," "funny/serious," and "safe/disturbing") let you shape this site's recommendations.