And of course there is the current official title holder, the Koenigsegg CCR (392km/hr).
A little bit after that Barbrus came out with the Barbrus TKR which supposedly goes up to 430KM/hr and does the 0-100 in less than 2 seconds (faster than an F1 car).
While the Barbrus has never been officially tested, there is an American company now aiming for the title, with this:
The SSC Ultimate Aero TT is trying to beat the Koenigsegg CCR's official speed of 392km/hr. Winding Road reports that Junus Khan, SSC’s marketing director recently admited that the company has managed speeds of up to 389km/hr.
However the car apparently has only ever deployed 71 per cent of its available power to reach those speeds. The Americans look determined the beat the CCR's time, when will bugatti and barbrus authenticate their claims? In an episode of Top Gear, James May apparently took the car to over 400km/hr.