Poll Everywhere looks like an interesting idea for schools or other presentation focused businesses or organizations.

Plus it's got a sweet promo video produced by Adam Lisagor's Sandwich Video:

Direct link to video

I really like that they include the ability to embed a result live in a Keynote or Powerpoint presentation so that you don't have to switch out to a web page mid-presentation. Also, Canada is included in their list of short code supported countries.

Pricing will either look crazy to you ("What? Why would I pay a monthly fee to ask people something?") or be a tremendous value to you if you've ever had to pay for, setup and configure a polling system.

Poll Everywhere