As released by the Bethesda Blog, a list of the top Oblivion DLC has come out. According to the blog post, "To this day, 2 years later. Looking at our Xbox Live reports, every day, tens of thousands of people STILL play Oblivion and they purchase thousands and thousands of downloadable content - again, every day. Yes, even Horse Armor continues to sell daily."
Not shocking that many people still play Oblivion. Shocking that Horse Armor still sells daily - as it's ranked number 9 on the list. I would of thought the Shivering Isles expansion would have been at the top of the list, instead it ranks only one higher than the Horse Armor.
Here is the complete list: