TIME has published an accessible feature called The 20 Most Influential Americans of All Time.
The Discovery Channel published a similar project a few years back (that link is to its Wikipedia page that shows their list — they took the original neat website off-line).
Here’s the simple assignment I gave my students using it (and, the next time I teach U.S. History, I’ll add the TIME piece, too):
A television channel did a poll to find out who people thought were the Greatest Americans, and then ranked them from the most important to the one hundredth most important.
Think about all the Americans we have studied so far. Pick who you think are the top five Americans and rank them one-through-five. Find a picture of them, write about what you think was their major accomplishment, and explain why you ranked them where you did.