I finally got around to listing some books on Amazon as chiricahuagal suggested. Well - so far so good!! I put up all my listings yesterday and already, two of the books have sold.
But you're not just limited to just books. It looks like you can selling anything as long as there is an item page on Amazon; just click the "Sell Yours" button. If Amazon doesn't have a listing for a particular item, you can sell in the auction section. Amazon is virtually an online pawn shop in that regard.