Before launching off onto my own, I worked at a major management consulting firm.  One of my big projects at the Firm was to figure out new and innovative communication techniques, the more interaction the better.  Our studies had shown that clients were sick of being spoken at and wanted to be spoken with.  (Not too revolutionary if you think about it)

One of the tools we found out about was something that we called Consensor, but is thankfully manufactured by many and are called audience response systems, commercially.  They are not unlike the voting panels that you see on TV game shows, like Who Wants to Be a Millionaire.  Basically, you give each audience member a little electronic tablet that they can use to answer questions you put on the screen.  Once you hit the “ready” button, their responses are then projected on the screen.  It’s a really fabulous way to get a huge group of people involved in your content.  Also especially helpful for more introverted groups that are less likely to jump up and ask questions in front of your crowd.

These services do cost a little bit, though, so make sure you have the budget!  And absolutely use the on-site technician, you never know what can happen with more moving parts.

I looked up a few commercially available services (note that I have no used them so cannot talk to how effective they are):

Opinion Technologies

Interactive Meetings