/Worldcat has released a pretty amazing list of the top 1.000 books owned by libraries around the world.
Truth be told though: not every libraries holdings are represented in Worldcat, but the number of libraries is pretty big. The list has a heavy english-language/western slant as can be expected.
Before you look take the time to think about the top 10 and see how many you guess right. I'll give you one: the bible is in there, but it's not where you expect.
Ready? Top 1000.
For added fun check the factoids section as well. Cool stuff.