I have sold some on half.com before. It wasn't bad. Amazon was OK too. I've not sure about DVDs etc., but ebay is really not good for books unless maybe something rare/collectible.
If you are more interested in getting rid of them than making money off them, see if there's a Freecycle group on your area (see http://www.freecycle.org
). I dumped several grocery bags of books that way.