From here:The game may have shipped last month, but the team has been busy building fresh new content! Extend your Need for Speed ProStreet experience with this FREE download, coming in mid-December to Xbox® LIVE Marketplace, PLAYSTATION®STORE, and the EA Store. The extender pack features two brand new tracks (Leipzig Test Track & Japan's Tokyo Expressway) and additional cars (Plymouth Road Runner & SEAT Leon Cupra)! You'll also have the ability to purchase new high-end dream cars such as the McLaren F1, Aston Martin DBR9, and the Bugatti Veyron 16.4, which is making its video game debut in Need for Speed ProStreet.
http://www.ea.com/prostreet/downloads.jsp
Apparently it's going to be a free download, and out soon .