Here's a few more:

A couple of towns in Canada, Lloydminster and Regina, and a historic old hotel in Toronto, Le Royal Meridien King Edward Hotel. (was Canada still a british Commonwealth in 1903?)

The ratification of the Panama Canal Treaty (British shipping no longer had to go around Cape Horn to reach the Pacific).

The incorporation of the Ford Motor Company.

And, most importantly of all, the Centennial Celebration of the first World Series played between the Boston Pilgrims and Pittsburgh Pirates in 1903!