I have always been fascinated with the impact of people's encroachment on forest and jungles. The misuse of land has caused people to come into contact with biological elements, such as viruses, that we had never been exposed to before, on such a large scale level. Disease such as Ebola and Aids have emerged from the jungle to impact our society. Also the method in which viruses from these remote regions have spread is interesting.
If you're just looking for ideas, try to tie it to current events. How about the geology of oil, or the science for cleaning up oil spills? How about volcanic eruptions like the one in Iceland recently? The curious deaths of so many honeybee hives? It could be almost anything you are interested in that others also have recently heard about. It will naturally draw their attention to your exhibit.
I would take the thing about which you *don't* know a whole lot, but are curious about. What sounds fascinating to you? Genetic engineering? Black holes? Black matter? Make it a learning experience!
The impressiveness of your chart is going to be directly related to how well you know your topic and how thoroughly and entertainingly you present it.
What interests you? What topics do you know the best - know the most about?
While presenting a difficult topic may look impressive, it will fail if you do not master it. My advice is to master something that you already have a pretty good grasp of.