In Star Trek, when Spock landed on an unfamiliar planet he pulled out his trusty tricorder to scientifically analyze the world around him.
"Tricorder" is an Android app that, rather amazingly, allows you to do the same thing.
It's a lot of fun to see the data pouring out of the phone's amazing set of sensors (accelerometers, magnetic field, microphone, GPS, network speed, etc.). The GPS view also shows a nifty compass.
You can read more about Tricorder at http://code.google.com/p/moonblink/wiki/Tricorder.