Quibblo is another easy quizzing/polling site; like Twiigs, they have a good breakdown of categories to choose from if you are looking for a poll. Here's the description from Quibblo's website:

Given the way the results are displayed, I can see this as a usefull overall assessment tool (i.e., is the class as a whole getting a particular concept?). A typical quiz would look like this:

And the results would look like this: