Regardless of your politics, this chart is a great example of how data can tell a story. It's a very simple graph by the Pew Forum on Religious and Public Life showing the changing attitudes about same-sex marriage. It shows that in the past couple of years, people have begun to be in favor of same-sex marriage.
I'm showing this chart because it so clearly represents the story of the data. The eye is immediately drawn to where the "oppose" and "favor" lines cross. Other obvious choices for this data would have been a stacked bar chart or a side by side bar chart as shown here (which I created with the source data just as examples):
These two charts are fine, but they really don't tell the story of what's happening. They merely present the data. The viewer has to take the time to look at each year and detect the year where there's a flip. The flip is much harder to see in these two graphs.
It goes to show that even in the most humble charts, we must choose wisely to convey our message.