This has become my new favorite question to ask job candidates:
Tell me about something you achieved that you think someone else in your same job would not have gotten done.
It's basically the flip side of what I tell job-seekers to do on their resumes.
It's an awesome question, because you can immediately see if the person operates in a way where they're naturally pushing to do better and better, or if they're content with just doing the basics. It tells you about resourcefulness, drive, initiative, the bar they hold themselves to, and their general approach to work.
I love it so much that there's a danger I may start using it on dates, etc.