Metacritic

Metacritic is a lot like Rotten Tomatoes, only it covers more than movies. I really love this site. You can see what most critics are rating something at a glance, and the list on the left with the scores right by the names is really convenient. Also, you have to check out the all-time worst and best lists, located at the upper-left for each media section. Last time I checked, Kevin Federline's album had the absolute worst overall score in the music reviews.