An interesting question.
In America (the United States), we drive on the right side of the road, opposed to Europe and Asia.
The reasoning for driving on the left side of the road is interesting. During the Middle Ages where fighting with swords took place on horseback, most people were right handed. So, they would charge on the left side of a dirt road, and slash at their opponents with their right hand. Interesting to know.
About 72% of the world's total road distance carries traffic on the right, and 28% on the left.
As a fan of general discussions regarding different customs, Wikipedia's charts and images regarding countries that drive on which side of the road is interesting. I never knew that the United States used to drive on the left side of the road before switching to the right. Of course, as most of North America was considered British colonies, I'm not exactly surprised that British customs changed.