WP-Polls adds an AJAX poll system to your WordPress blog. You can easily include a poll into your WordPress’s blog post/page. WP-Polls is extremely customizable via templates and css styles and there are tons of options for you to choose to ensure that WP-Polls runs the way you wanted. It now supports multiple selection of answers.

Pricing: Free
Requirements: Wordpress 1.5+
Source: http://lesterchan.net/wordpress/readme/wp-polls.html