As more and more schools are now looking for integrating clickers with Moodle LMS, I think it's time for Moodle HQ to seriously consider develop such plugin (could be in a form or block, or integrate with the current "choice" module. I did a search on the 3rd party Modules and plugins database on moodle.org/mod/data/view.php?id=6009 and here in this tracker, but didn't find any.
Some of the most popular "clickers" are:
eInstruction CPS (http://www.einstruction.com/products/student-response-systems)
TurningPoint - seems to have some sort of Moodle integration done: http://www.turningtechnologies.com/studentresponsesystems/lmscontentintegration/