What should i do with all my standard DVD's now?

[Valkyr47]

I started off by telling myself i would not repurchase anything i already had in DVD because i HATE double dipping, but as my Blu-Ray collection has been growing, and considering i own about 700 dvd's and most of those are pretty popular movies such as dark knight, transformers, etc, its almost impossible to not double dip or i would be missing out on a lot of awesome movies on the new format

What have you guys done with all your DVD versions of the movies you bought on blu ray?

i will keep the dvds for movies not out on blu ray yet or that i havent bought, but i dont see the point in having a movie take up 2 spaces on my shelf, especially when one is completely inferior to the newer product

do people buy second hand dvds? craigslist? ebay?

any ideas?