Here's what I do in either position (audience or speaker):

Speaker:

"No questions? Okay then, I have a question for you. Show of hands if you've ever heard...." - and then you ask something that's a misconception about your work, or a current rumor in your field, etc. By asking for a show of hands, no one has to be the first to use their voice, people raise hands and feel like they're participating, you're still commanding their attention, and usually the topic can spark a few minutes of dialog. Make sure you have and end point to that, like: "... The reality is that we still don't know. And this is something I'm planning to incorporate into future research/work/whatever."

Audience member:

During the talk, I ALWAYS come up with a question based on one of their slides or points. A genuine question, not 'what did you say about this one thing before?' Or if you can't come up with a really good one, then ask where they see this going in the future, what their next step will be if they didn't mention it, if they can see alternate applications for it, etc. YOU be the person who saves the speaker from crickets. Often your question will make their day, save their ass, make their boss/advisor proud that they got a question, make your boss/advisor impressed that you were paying attention and engaged. --> Always be the person who has a question at the end.