Regardless, the EU's latest ruling will ban the current R-134a coolant starting in 2011 for both new vehicles and aftermarket solutions. At present, there isn't a commercially available alternative that's ready to use in our current A/C systems, but there are a number of new chemical formulations currently being tested.
One interesting alternative is carbon dioxide, the same greenhouse gas that internal combustion engines emit when burning fuels. If used in car A/C units, the CO2 would need to be stored at extremely high pressures to be effective. Although CO2 does contribute to global warming, conventional hydrofluorocarbons are considerably worse.
[Source: Autocar, Guardian]