The Fisker Karma is a luxury sedan powered by a series hybrid gas/electric drivetrain. The creators of the Karma decided to address the common complaint about electric cars' silence at low speeds, by installing a system that plays "Tron"-like noises based on the car's speed and acceleration. Uber cool!
Here's what it sounds like idling:
And here, it goes 0-60mph on the track:
I don't know of any other production vehicles that are making noises like this, but I hope to see many more!