Does your audience tweet?
Then you can ask for their opinion and displaying their tweets directly in your PowerPoint slides.
Poll Everywhere is the easiest way to gather live responses in any venues such as conferences, presentations, classrooms etc. 
Poll Everywhere helps the audience to tweet a short comment directly to your slide in real-time.The interesting feature is that you can leave your audience with multiple ways of votting through Twitter,Mobile etc.
You can also analyze the results visually through as the audience vote for it.
Credit:Poll Everywhere