I don’t use one at the moment but I did have a look at WP-polls. It’s looks quite good. I tried integrating it but since I use a hard-coded sidebar (instead of widget based) it becomes quite a task!
You could have a look at a poll service such as Poll-Daddy which can be integrated quite easily although most people recommend WP-polls because it’s apparently much easier to include the polls, not just in the sidebar, but in any post…
I haven’t heard of many alternatives to WP-polls… That’s not to say they don’t exist though.
I use Wp-Polls. I used it when I had my visitors decide on my new design and it worked quite nice, EXCEPT, when I asked the people I worked with to vote they couldn’t. Problem is we were all on the same network, so only one person could vote (at work), and once they did, that was it. :( Not sure if you get the same result with people on school connections/libraries/etc, but it was kinda sucky.