Are you looking for a FREE tool that will allow you to poll students/participants and let them ask questions and then social rank those questions in live time? Sli.do is an easy-to-use, device agnostic (works on any device), audience polling technology that is my current favorite for large and small audience interaction. Teachers can use it for free with audiences of up to 1000 people. Simply create an account, create your event, and then ask your participants to log in and ask/rank questions or answer polls, too easy! You will be up and running in just a few minutes. If you have any questions, I would be happy to demo it for you and share how I have used it. Or, if you would simply like to give it a try, here are a few videos to give you a little more information.
Managing Questions in Sli.do
Managing Polls in Sli.do