“Everybody is searching for bigger and bigger data: how about this? A comprehensive list of every event in human history.”
Even though this isn’t library data, it’s the sort of thing that libraries might be interested in; if for no other reason than it could be a fantastic resource for reference librarians.
More information is available on The Guardian’s Data Blog.
The National Library of NZ has released some data sets under an open license.
You can get access via the API to data about their national publication set and their digital collections, including old newspapers (in the past papers set).
More sets will be released in due course.
Some relevance for libraries here