Which questions invite discussion best?

Which questions have you asked that generated a thought-provoking discussion?  Please leave answers in the Comments. 

Here are some questions I have used in the past to gather feedback.  Some of these originate from Thomas Angelo and Patricia Cross's Classroom Assessment Techniques, which is printed by Jossey-Bass.

• What's the most important thing you learned today?
• What questions do you have that remain unanswered?
• What is the muddiest point?
• What would you like to learn today?

Not sure if I have asked some of these others, but they seem like good ones:

• How does this apply to your own life?
• How can this information be applied outside of this class?
• How do you find research for your college papers?
• What makes a source good and/or reliable?  What makes it worth using?
• What is a reference resource?  Why would you want to use one?
• What is the difference between popular and scholarly articles?  Between newspaper/magazines and academic journals

Here are some questions that may be good to ask with audience response systems, clickers, or text messaging software:

• Have you searched for books in our catalog?
• Have you searched for books on the shelves?
• Have you found articles in the library databases?
• How can you typically distinguish the journal title or book title from the rest of the cited reference?
• What makes a source good and/or reliable? What makes it worth using?