Here are some suggestions:

Bored and Confused is a new tool for getting audience feedback during a presentation.

Mentimeter is another one.

Here are others.

Adding Interaction into Presentations is from CristinaSkyBox.

Quest Up looks like a neat new tool for creating “back channels” when giving presentations.

Questionwave lets you interact with an audience when speaking live to them.

When You Get Nothing But Crickets gives you advice on what questions to ask…