I've been giving my students in my human nature courses an assignment to find good aphorisms and quotations that offer deep insight into human nature. If you're curious about what these persons have found and shared, I've uploaded their collections to some web pages I'm willing to share.
Here are some quotations gathered by students in this semester's course.
Here are some older collections of quotations from the summer of 2007, and here are even older ones from the spring of 2007.
If you look over these you can see how some students find quotations from the readings I've suggested or forced them to read in my course, while others mainly find quotations by going to websites that specialize in providing quotations on whatever topic you suggest. Some students diligently give good citations and a personal interpretation for each quotations, while others just throw out quotations with barely any citation and no personal commentary. If you look past that to the quotations they have selected, there are some really beautiful and thought-provoking gems of insight among the aphorisms and quotations collected here.