Try to engage the audience

A central purpose of a presentation is to get comments from the audience.  This benefits the speaker in two ways: 1) it may help in your research, and 2) it may help you in future presentations.  

A great outcome is when audience members can make comments that get you thinking, bring in facts from new disciplines, etc.  Audience participation can enhance your future research.  Additionally, audience comments will give you insight about what they are following, what they've learned from the presentation, and where they are confused.  This is valuable input for the next time you give the presentation.  Every presentation should get better each time you give it.

The problem is that most audiences have gotten accustomed to sitting by silently and deferring questions until the very end of the talk (by which time most questions are forgotten or are no longer relevant).  As a speaker you need to shake them out of this stupor early in the talk.  Pose questions, ask them about their familiarity with the subject at the beginning of the talk, find out about the distribution of expertise in the audience, etc.  Another thing you can do is conspire with a friend or two and have them pose a question or two during your talk.  Once someone breaks the ice, a lively discussion is possible.  David Stern of the Howard Hughes Institute has even suggested mixing in a few blank slides just to shake up the audience and tell them this is a time for interaction.  I've never done it, but it is worth a try!