I usually go to amazon.com, type in books I am interested in, and find the reviews and other recommendations.
If you're interested in classics http://funadvice.com/r/bjtjgfm57
oprah's book club has some amazing books.. i just read a book by ann-marie macdonald called as the crow flies..excellent..
Try ebay.com and see what happens there.Hope that helps.
commonsensemedia.com is a good one. it has everything