What are some good topics for a short documentary?

I like making short documentaries (10-20 minutes) and I have made some good ones in the past such as one about history of KFC and about the BART shooting of Oscar Grant. However, I need new topics so I can stay busy with filmmaking all the time. I am thinking I should do either something political, something that would be funny, or a controversial topic but I need specific topic ideas for the docu film. Any ideas?