If you want a WordPress plugin developed from scratch then please get in touch.
Below is a plugin we developed for tomorrowtimes.com.[hr]
WP-Predict enables you to add multiple choice questions to your blog posts. Your readers can then select an answer. Once you set the answer your readers will be ranked in a leaderboard widget.
You can download the plugin from wordpress.org here wp-predict.
Here are some screen shots of the plugin in action
[hr] The back-end