Most ratings plugins contain too much code: inline JavaScript, messy markup, weird CSS. Rate is simple, hardly intrusive, and completely overridable.

A Post/Page/Custom Post Type’s rating is the average of all comment ratings. A user can leave a rating when commenting, and change that rating inline after leaving a comment (if logged-in or Cookie’d).

Don’t be afraid to play around and extend the code: drop a rate.css file in your theme directory and mine won’t even load (by default, Rate stars are transparent with a white border, so you can use background-color to set your stars’ colors)!

<?php 
// in this version, you need to insert these functions into your theme for ratings to appear
// you don't have to use the_rating(), the comment_rating() will work by itself, but the_rating() will not

// for a Post, Page, or Custom Post Type (average of all comment ratings)
the_rating();

// for a comment
the_comment_rating();
?>

Read More: http://scottctaylor.wordpress.com/2010/11/30/new-plugin-rate/