I recently read an interesting article from space.com on Y! about how the moon's surface may contain secrets of Earth from a few million+ years ago (and possibly Venus, also).
When we studied the moonrocks brought back from the Apollo missions, we found that the surface of the moon contains very, very old rock. On earth, atmosphere and tectonic activity constantly buries layers of soil below, but the moon has neither atmosphere nor tectonic activity, so its surface hasn't moved much over centuries.
Anyway, the article suggests that when earth was hit by large asteroids (like those that may of killed the dinosaurs), pieces of soil may of actually been launched fast enough to hit and lie on the surface of the moon. Scientists could study these "ancient earth soil samples" and give us a better clue of how the earth was before the asteroid hit.
There is also speculation that the moon could contain soil from venus (which we won't be able to study anytime soon, due to its extrodinary high surface temperatures), which would give planetary geologists a great artifact to study.
So, to try and find these rocks would require a trip to the moon. Something not done since the 70s. I'd think that a 'mars rover'-like robotic experiment may be a good way to accomplish this. Create a robot that could be used on other planets (like Mars) that will scour the rocks in search of "planetary asteroid debris".
Anywho, I found the article to be a fun read. Here's hoping we see another man on the moon, soon.