AnswerGarden is a very useful web application that can be embedded into a website. I use the embedded widget for feedback on one of my websites, but it can be used for a variety of purposes such as a guestbook or poll. It is available for free.
If you have a website there are times when you feel the need to set up a poll or a survey to gauge your visitors opinion/s on a certain subject/s. Polldaddy has a number of options for doing this, including a free one.