Snapshot of Television Use in the US (Nielsen)
Nielsen data comes at a high price for advertisers and academics alike. The former group can pay; the later group in most cases has to wait under the table for the crumbs to fall as general ratings and rankings are reported in secondary sources. Then there are the occasional reports Nielsen releases such as Snapshot of Television Use in the US (September 2010). It's not very big but there is some good info packed into it. Besides list of top ten shows for 2009-2010 which you can get a lot of places, you'll find comparisons of the size of the broadcast season audience over the last few years; viewing by genre; viewing by source (broadcast, public, ad-cable, premium cable, and other cable); and HD and DVR penetration.