So I decided to update it, mostly because Amazon now has an API and I wanted to play with that. So now you can go to the DVD price comparison tool page, enter a DVD name (TV shows on DVD work too...include a number to find a particular season/volume). In the results you will get the top Amazon.com matches, and I compare the top match from that to the top match from Deep Discount.
The result is pretty good...here's a search for the recently released Casino Royale. And the search from my original post about the tool still works: Airplane: The "Don't Call Me Shirley" edition.
As before, let me know if you want me to add another site to compare to. Best Buy's website is still a pain in the ass (and nearly always more expensive).