The US, UK and more Harry Potter Audiobooks (1-6) are on the itunes top seller lists for their respective site.

US:
3:   Harry Potter and the Sorcere’s Stone (Book 1)
4:   Harry Potter and the Half-Blood Prince (Book 6)
8:   Harry Potter and the Chamber of Secrets (Book 2)
13: Harry Potter and the Prisoner of Azkaban (Book 3)
14: Harry Potter and the Goblet of Fire (Book 4)
16: Harry Potter and the Order of the Phoenix (Book 5)

UK:
11: Harry Potter and the Philiosopher’s Stone (Book 1)
14: Harry Potter and the Chamber of Secrets (Book 2)
21: Harry Potter and the Prisoner of Azkaban (Book 3)
45: Harry Potter and the Goblet of Fire (Book 4)
53: Harry Potter and the Half-Blood Prince (Book 6)
59: Harry Potter and the Order of the Phoenix (Book 5)

For other countries lists click Read More!
I dont know where you can find the whole list because my source for the news didnt post it and I cant find it. If you can find it comment with the link or email me.
Thanks In Honor of Rowling.