http://www.imdb.com/title/tt1261945/

Even though it's not out til next year, from spoiler pics we can already add a featured car.
http://www.egmcartech.com/2009/09/02/spy-shots-new-mercedes-benz-e-class-convertible-spotted-on-sex-and-the-city-sequel-set/

It's the new 2011 Mercedes E550 Convertible (W212)

I had finally found a shot that revealed the rear badge
http://justjared.buzznet.com/photo-gallery/2178992/sarah-jessica-parker-satc-sequel-17/