I think ebay is the best way to sell your unwanted workout dvds. Especially if they are Cathe's they sell pretty well. Of course, be sure you want to sell them...because way back when....after I had pre-ordered the GymStyle set, there were a few I thought I did not want, and now I wish I still had them!
If you are interested, I have a lot of workout DVD's (not Cathe) that I would be willing to trade for Cathe. I am new to her so I don't mind anything! Even her old stuff! I can give you list of DVD's I own, but mostly Bob Harper, Jillian Michaels and Jackie Warner. I have one Billy Blanks that didn't really fly with me so now it's sitting on my shelf collection dust. The DVD's are in excellent condition and all come with a case. Let me know