This is a great question. Let me offer some suggestions.
First, to get some ideas, you might want to do an Internet search about pictures of the year. The New York Times, CNN and other media companies usually have photos of the year. These pictures can inspire you and give you many ideas.
Second, you want want to consider what people are going through now. The benefit of this approach is that there is immediacy. In other words, things will be fresh in their mind. This might help a lot if there are no captions. Some popular topics will be 911, the economic crisis, Occupy Wall Street, and the presidential election.
Third, you might want to create a sequence of pictures to tell as story. Test these pictures on friends to see if they can get your story.