Michael Hyatt, CEO of Thomas Nelson Publishers, just wrote a great post on creating a better bestseller list, especially one that counts Christian books. Read more about his post here: Toward a Better Bestseller List.
Earlier he wrote a post on why bestseller lists are inaccurate. You can read that here: Why Bestseller Lists Are Inaccurate.
Here's another great discussion of the flaws inherent in many of the major bestseller lists: Bestseller Lists.