Apple has released an official Find my iPhone app, and it's a universal binary for both iPhone and iPad. (Yes, it's still called Find my iPhone on the iPad and iPod touch, what's in a name?)
It works pretty much as you'd expect -- enter your MobileMe login (it asks for the password each time, which might annoy you until you realize someone could use it to track you or your family members), see a list of your devices, tap one to locate it, send it an alert, lock it, or remotely wipe it.
I couldn't get locate or alert working in my quick tests, but it could still be rolling out. I'll try again later. If you installed it, let me know how it's working for you.
iPad screenshot after the break.