It’s relatively easy to find the top rated TV shows for a given week. However, I’ve had a problem finding the overall viewership for a given time (such as 4pm on a Thursday). Is there anywhere they give the numbers for all TV sets turned on at a given time for all times of the week?
I don’t think the “real” ratings (Nielsens) are publicly available. Informal ratings (like from cable companies) are more common and usually free. Also, you have to watch out for completely fabricated numbers. The Drudge Report, for example, pulls numbers out of their ass at random, probably by how much sponsor money that tv station gives them.
Superhal is correct, TV stations pay for Nielsen and radio pays for Arbitron ratings. So both companies have pretty strict rules about posting the information. A station doesn’t get a rating unless it pays the company for it. And of course without those numbers it’s hard to sell ad time.