Sexy Vote is a jQuery plugin that allows you to easily embed voting system on your web site. The only thing you should do is to write $("#vote").sexyVote(), and the rest of work will be done for you! Ah yes, you should also write callback function that will respond to user's voting (it will probably handle saving the vote on the server via AJAX request), but it's quite easy to write it. You can also configure plugin to customize its appearance. If you will like this plugin, please vote for it! :)

Resources:

http://vladimir-k.blogspot.com/2008/12/why-commenting-is-not-enough.html - home page

http://phone.witamean.net/sexy-vote/ - demo page

http://plugins.jquery.com/project/sexy-vote - Sexy Vote in jQuery plugins directory