To me, the answer is 'virtually any'. And HP wants us to believe that, too.
But, I'm always intrigued by the dissonance between the content HP tells us is verboten, or at least likely to get a hub flagged for review, and what actually appears - and rates well.
Specifically, sometime when you're a bit bored, take a look under the Books, Writing and Literature section, (and its sub-sections). Click on the 'best' tabs, and if you're like me, be amazed at how many longstanding hubs that qualify for 'best' rating are simply collections of quotes, by famous people.
By definition, a quotation from someone else, must be copied, and many (if not all) are widely duplicated all over the net.
Yet, HP tells us that 'original, informative, hubs offering new insights or previously unknown information' are the only ones that can be expected to reach the exalted heights of 'best in category'.
Go figure. :)