There's a whole lot of articles out there talking about the recent surge in exposure that SIRIUS Satellite Radio is getting, but out of all of them this article by The Journal News sums it up with the most amount of detail.
Comparing not only the new (or upcoming) content, but also the OEM car distribution as well as satellite configuration and receiver technology, this is a great read for those who are still on the fence between the two providers.
The link doesn't work :(