Answer Garden provides a simple and interesting way to get feedback. Responses (which must be 20 characters or less) are added to a word cloud. Create your question, very easily (no registration is required) by entering your question and clicking Create, you can then note the url or embed code. 
As people post responses the word cloud will develop. (Click on the word cloud link to give your favourite Web 2.0 tool!). Hovering over a response gives the number of people who have made that response. It is possible to change settings such as colour but it is not necessary to do so.
Using Google Forms provides a way to get feedback from a group of people, their responses are all returned to a single spreadsheet. See the Commoncraft video here.
A comprehensive manual can be downloaded here.
Also see Interesting Ways to Use Google Forms in the Classroom from Tom Barrett’s Interesting Ways Series.
For an examples of forms see this one used to collect student self-assessments of their PLTS skills development in Mathematics and this to collect student responses to some questions on learning using various digital tools.
Power League from Futurelab allows students to sample opinions. They can take part in published leagues such as this on the important factors to consider when designing a new school or create their own.
Urtak provides a simple way to create a survey where the responses to all questions are yes/no/don’t care. See this example on student use of a wiki. The FAQ page provides useful information on the tool.
