Carlos Moreira on "Plugin for community"

Hello
there are a lot of plugins for this.
Check for example this ones:

http://wordpress.org/extend/plugins/wti-like-post/screenshots/
http://wordpress.org/extend/plugins/like-dislike-counter-for-posts-pages-and-comments/

If you search for 'rating wordpress plugin' or 'star wordpress plugin' or 'like dislike wordpress plugin' you'll find a few options that might fit your needs.