(Deutsche Version des Artikels)
When you want or need to start surveys within your (WordPress-)blog, you can use a nice poll-plugin named Democracy for this task.
There exist negative posts about that tool, like the one at blog-republic.com, but it has to do with the older version of this app and one can do something about the Duplicate-Content-issues as well: A very simple workaround would be to use JavaScript for submitting the poll (via OnClick).
Within the comments to that post the author of the plugin even said, he would rewrite the tool. So one would have to examine the actual version of the tool thoroughly.
The english 2.0.1 version is the most up to date verson.
Greets,
Lestarte