How much do your tweets say about you and your interests? BookRx recommends books and categories that you might find interesting by analyzing your Twitter activity. Just pop in a Twitter handle (no registration or linking to your account needed, so you can try this out with anyone - may be really helpful if you're desperate for a last minute present!) and it will come back with suggestions for you. I hadn't read any of the books that it suggested for me, but there were several there which did look interesting. It did however get my interests fairly close - Business, Sports, Science Fiction, Technology and Politics.
It worked very quickly and links you to the books on Amazon.com if you're interested in looking at them in more detail.