One of the first bits of DLC is the game's E3 2011 interactive demo. This was originally meant to show off the visual capabilities of the Vita. The downloadable version of the demo will be released for free on the 22nd. It runs as its own app and can be downloaded even by those who don't have the game.
The base version of Ridge Racer includes five cars and three courses. Here are some images from the official site.