This InfoGraphic is simple, easy to read, and user-friendly as it allows people to search different topics over the past 200 years.

http://www.fastcodesign.com/1662912/infographic-of-the-day-google-uses-200-years-of-books-to-track-our-culture

I also found this to be very informative in regards to the political climate over the last decade. I like the level of interactivity.

http://awesome.good.is/transparency/web/1010/political-climate-chart/interactive.html