What software can I use to poll my audience during presentation? I recently attended a lecture where the speaker used piece of software to interactively poll the audience and display the results. The particular solution was ResponseWare. What other solutions are available? Worth the money (if paid)? Pros and cons? 

Please note, that I'm not interested in top 5 results of Google search.. I'd be more interested to hear personal experiences with specific software, both as a presenter or audience.
The Software Carpentry instructors do lots of presentations where they need/expect rapid, interactive feedback. They (especially Greg Wilson) have lots of experience of different ways of doing this. Note that their current method, that works extremely well, is to use different coloured sticky notes.

I haven't seen a technical solution that worked better; most are considerably worse. However, this is only practical for yes/no or multiple choice polls.