Where can I find information (namely ratings) about TV shows?

The kind of information I am looking for is about how successful a show is. The kind of ratings I want to see are the kind that I hear TV show host talk about "the ratings just came in", etc; NOT V-chip ratings. If graphs exist of ratings over time I would find that interesting. I would also like to know what is the most popular TV on a particular station/ network/ channel, and also most popular show per time block. Thank you.