I would go the Columbiahouse route. They have a huge selection of titles. I can usually average ~7-8 bucks per DVD brand new. You just have to know how to play the system correctly.
1)Find a better code for your order. (DVDTalk.com has a great thread for this)
2)Order the expensive titles for your introductory package.
3)Preorder your 2 commitment movies required as 19.95 titles.
4)Close the account.
I have ordered hundreds of DVDs through Columbiahouse. The have always been easy to deal with and provide excellent DVDs cheap. You can have 2 accounts set up simulaneously at one address. I used to do this to build my collection, but now normally open them one at a time. If you don't mind waiting 2-3 months to get the newest releases, the prices can't be beaten. You can catch a few e-tailers with good deals once in a while, but they have really died off. Reel.com is now out of business, but used to have some really great deals when DVDs first came out. I buy about 75% of DVDs from Columbiahouse, 20% from DeepDiscountDVD.com, and 5% other places. BlockBuster and anyone else selling used DVDs for more than I can get them new through CH can kiss my ***. I don't buy used DVDs. It's like a box of chocolates.