Via TV, CSPAN has been the best. Very little commentary, and none during any events.
Via Web, CBS webcast has been excellent most of the time. Absolutely no commentary and no banners or logos. Sometimes the image is a bit pixelized, but for high speed internet, usually pretty good. [It also runs about 5 second behind the CSPAN feed. They both seem to be using 'pool cameras.'
CBS feed is great, getting DirectX captures with Hypersnap