A modified version of the Toyota Prius and Audi TT driving itself around the west coast.
Quote from the Google blog post:
Our automated cars, manned by trained operators, just drove from our Mountain View campus to our Santa Monica office and on to Hollywood Boulevard. They’ve driven down Lombard Street, crossed the Golden Gate bridge, navigated the Pacific Coast Highway, and even made it all the way around Lake Tahoe. All in all, our self-driving cars have logged over 140,000 miles. We think this is a first in robotics research.

Picture credit: Gizmodo, Techcrunch and New York Times
Updated with a video: