The company founded in April 1996 that has been providing "Free web traffic metrics, top sites lists, site demographics, hot urls, and more", have just launched a "User Reviews" section to there very informative site, letting users (and webmasters alike) rate and review the sites they own.. I mean visit.
Although you do need to be logged in before you are able to rate and review a website, you don't need to register an account with Alexa, you can simply "Connect with facebook"
Don't have a facebook account? then its time to come out of that rock you've been living under and get one :D