Bestselling Used Books on AbeBooks Since 2000:

26. The Hobbit by J.R.R. Tolkien
94. The Silmarillion by J.R.R. Tolkien

I may have missed it, but I didn't see LotRs on there. Kind of strange, what with The Silmarillion making it onto the list.

BH

EDIT: Yeh, sorry, forgot to post the actual link. Provided below by Urulöké.