This one seems to emanate from Modern Library and tilt toward American literature. I don't think I'll ever understand why so many such lists put Ulysses at the top. Still, it's fun to browse these things. I think I've only read 32 of these, and I found several that I hadn't considered and will put on my neverending list of BooksToRead.
Via The Centered Librarian.
Update: Pietr Hitzig discovered that this book list has been heavily criticized.