And the winner is...

Adrienne!

She kinda had it in the bag anyway, as I owe her some RJ's licorice I gave her the head's up as soon as I posted.
Prize delivery may take some time, click here for status updates.

So here's the website where I got this map from:
http://users.pandora.be/worldstandards/driving on the left.htm

Some interesting history for you:

Back in the old country (Britain), swordsmen preferred to keep their horses left in order to have their right sword arm nearer to an opponent.

Then in the 1700's as the American's began hauling loads with two horses wide, they sat on the left horse to allow their stronger right arm free to whip the horses. Therefore they drove the horses on the right to give them a better vision of oncoming traffic.

Before the French revolution in 1789 the aristocrats travelled on the left, forcing peasants over to the right. After the revolution, they preferred to keep a low profile and joined the rest of the French on the right side of the road.

Hitler ordered the Germans and Austrians to switch sides in 1938, and the mass export of American vehicles around this time caused much of the rest of the world to follow their lead.
Others simply wanted to alienate themselves from Mother England as much as possible so switched.
Unfortunately Japan was a bit too slow to get it's vehicle exports increased or we might have seen more countries still driving on the left.

Some countries who did want to change, but decided against it were:
Britain - the motion was defeated due to the immense cost and pride in their heritage.
Pakistan - They couldn't get the camels to understand the new system.

So anyway, well done Adrienne, and anybody else who had similar ideas but didn't voice them.
If you disagree with anything here, remember the old saying "I read it on the internet, it must be true".