When I sell cards in bulk, I usually go to a dealer. Alpha, Beta, Unlimited (www.abugames.com) offers a reasonably good price for cards, depending on what you have. If it's mostly commons or uncommons, you may not get a lot, but it is an option. Though any payment you receive will likely be through PayPal.
But yes, check out any online dealers, and look at their buylists. Others include Star City Games and Cool Stuff, Inc.