Very simple to use, but very versatile polling tool. You just create a question and add some options then share it with the people you want answers from. The great thing is that they can add extra options and add various pros and cons of each option as well as voting on the ones they like. This makes the whole process of polling much more open, social and interactive.
Here's a quick video showing how it works
Tricider is online polling with commenting and voting that supports shared brainstorming. Free. Registration is optional. Possible student feedback and classroom applications?