some time ago i concluded that the best way to avoid a speeding car coming straight at you is to jump straight upwards and tuck your legs in.
this is assuming it's coming really fast at you, and you've only got about a quarter of a second to react. going left or right is a bad idea, because the car is probably going left or right too, so you've got a 50% chance of getting hit anyway.
besides, it takes longer to dive off to one side, because the act of diving leaves your legs in the way of the onrushing vehicle. conversely, jumping straight up and tucking your legs in takes half the time. you'll get hit by the sloped windshield instead of the flat bumper, and will hopefully end up rolling over the roof instead of getting flung through the air.
and if you're feeling particularly kung-fuey, you can try kicking off the hood of the car as it reaches you, executing a forward flip mid-air as the car barrels underneath, and landing gracefully on the ground as the car morphs into a flaming fireball behind you. signing your hollywood contract should take place within a day or two.
i only mention this now, because it seems that Jeremy Clarkson on Top Gear implied something very similar when describing the latest lamborghini on Top Gear Season 12 Episode 1. i love it when my ideas get independent corroboration. :)