This service allows your visitors to vote for your website. It is easy to integrate the service into your web pages. There is no own webspace needed. Where’s the difference? The difference to other voting services is that every user can vote. The users do not need an account to submit their votes.

WP Topvotes

This Plugin let the visitor vote your site via a simple widget like the facebook "I like this" button.

Scott Taylor

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 <code>rate.css</code> 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 <code>background-color</code> to set your stars’ colors)!
<pre><code><?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();
?>
</code></pre>
Read More: http://scottctaylor.wordpress.com/2010/11/30/new-plugin-rate/

Rate

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

WP Topvotes vs Rate