As someone who used to do a lot of used DVD selling on Amazon and half, let me just tell you it's a buyer's market right now like I've never seen. I quit with the online stuff because after Amazon took their cut, there wasn't enough to really make it worth my while to do to the post office three times a week. Unless you're sitting on a bunch of rare, out of print titles or a bunch of Criterion stuff (and even that's going down,) the people suggesting you just sell them for $3/each are on the right track. With a glutted market, piss poor economy and Blu-Ray starting to make inroads, the time for getting a decent return on DVDs is over.