SCOTUS hearts Earth
This will pave the way for a whole host of innovative policy options. For example, scaling vehicle registration fees with fuel efficiency, mandatory fuel economy standards, various kinds of carbon taxes (and credits), and all sorts of good stuff. The decision removes one of the biggest obstacles to policy implementation.
The media is probably going to focus on the potential nation-wide impacts, but I don't think Congress or the White House will come up with anything interesting. Even if 2008 is a banner year for Democrats, the federal government probably isn't going to enact any interesting or effective environmental policy. Realistically, a positive role in in environmental policy for the federal government will be in funding capital projects and research, and as an experienced manager of data.
The states are a different story. The decision will (I think) allow state-EPAs to move forward with regional policies. For example, California can finally enact the fuel economy standards for which it has fought for so long, or Massachusetts can get more aggressive about wind power. Some of the states will do nothing, and some will try things that turn out to be dumb. However, some of them will have the will and the know-how to come enact policy with real promise. The ideas that work will be copied, eventually percolating upward to federal policy after a generation or so.
Hooray for Federalism!