although its part of ebay, I usually get rid of them at half.com. You can set your price and if it does not sell, it costs you nothing. they take 15% if it does sell.. The shipping allowance is pretty low, so figure each movie will cost you about $.50-$.75 extra to send it with tracking.
I recently bought the hangover. Movie blows, sold it on half.com for $18.99 + ship. I think I paid $14.30 when I bought it at best buy (it was actually less since it was part of $20 off $100), so after shipping I think I made money.. Too bad I can't get back the 2 hours I wasted..
Where half.com works well is the OOP stuff. I sold off my james bond box sets 2x(upgraded 3x now to bluray). Paid like $40-50 for for the sets and sold them for $200-$300 a pop.. Stuff like oop little shop of horrors sold for $150..