As you may know, for some time now The Book Depository has been giving away free ebooks (11k title, in fact).
Today they opened (with little fanfare) their long expected ebookstore. They're reporting that they have 340k titles, and that that is more than any other UK ebook retailer. The offered formats include Epub, PDF, and MSReader.
I checked, and I can't see the 340k titles. Even if I count the books available in more than 1 format separately, I'm only seeing about 200k titles, with about 3/4 being offered in PDF. That's probably becuase of regional restrictions, though.