The iClicker has a lot of users here at UVM. - student unit is low cost (about $30) - student uses AAA batteries, easily replaced - faculty receiver is cross platform (Macintosh, Windows. Not sure about Linux) - works with any software - http://iclicker.com/dnn/ - note: clickers here are purchased or rented by the student. Other options include cellphones - uses webhosting for polling - allows text imput - e.g. http://www.polleverywhere.com/