I have just implemented an article rating system. This was asked for by a few people who couldn't or didn't want to utilize the Facebook "likes", or the Google "+1" methods.
In the "header" of each article, there is a row of radio buttons labelled 1-5, with 5 being best, and 1 being worst. Simply select one of the radio buttons, and click the Rate This Article button.
Note that you can only vote for an article one time; this prevents abuse of the system.