This looks nice:
http://www.fyneworks.com/jquery/star-rating/
But you will need more of a backend to make sure people can't vote twice and to get an average of number of votes. The votes need to be stored somewhere (or at leas the current average) and whether or not a user voted already should be stored on the server too.
This link can tell you about some of the server-side stuff that needs to be done:
http://www.yvoschaap.com/index.php/weblog/css_star_rater_ajax_version/
