I am currently generating a list of alternatives to physical clickers in the classroom. I am testing a few out. One I liked that was free is Pinnion. I also want to explore using Google Docs Forms as a polling/survey tool in the classroom (it has a lot of potential) .  Here’s my list (feel free to try them out as well, each has their own style and features):

PollDaddy: http://polldaddy.com
Socrative: http://www.socrative.com/
Piazza: https://piazza.com/
LectureTools: http://www.lecturetools.com/
QuestionPress: http://www.questionpress.com/
Learning Catalytics: https://learningcatalytics.com/
polleverywhere: http://www.polleverywhere.com/highered-student-response-system
mentimeter: http://mentimeter.com/
Celly: http://cel.ly/
eClickers: http://www.eclicker.com/
TurningTechnologies ResponseWare: http://www.turningtechnologies.com/studentresponsesystems/mobiledistancelearning/higheredresponseware/
Socrative: http://socrative.com/#
Google Forms: docs.google.com
Top Hat Monocle: http://www.tophatmonocle.com/
GoSoapBox: http://gosoapbox.com/tour
iClicker Web Clicker:  http://www.iclicker.com/products/webclicker/
ClickerSchool Virtual Clicker by Eduware: http://itunes.apple.com/us/app/clickerschool-virtual-clicker/id444020820?mt=8
SodaHead Polls-WP plug-in:  http://wordpress.org/extend/plugins/sodahead-polls/
Pinnion: http://www.pinnion.com/