You can go to the firm yaya's and post in the swapmeet there. That is where I buy and trade 90% of my DVD's. You have to create an account to post and you may also want to say who you are on Cathe's site since your post count will be low. Here is a link to that board. http://firmbelivers.yuku.com/
You can also sell them on amazon. Just look up what you have to sell and to the right is Sell Yours? and you can click and list it. I prefer to buy and sell on amazon as opposed to ebay.
It seems like it's easier to sell on Amazon than on ebay - I think I'll try to unload some of my DVD's there. Seems like a lot simpler process than ebay, am I right?
I've sold and bought DVDs off of Amazon, and I think it's very easy. Also, I would suggest to go to videofitness.com if you are interested in trading - it's rather fun to do!