Australian Baseball League
This one may not be as surprising; several well-known MLB players have come out of Australia, including the Oakland Athletics' pitchers Travis Blackley and Grant Balfour. Baseball was -- surprise, surprise -- introduced to Australia by Americans. The founding myth claims it was American miners hungry for gold in Victoria in the 1850s who played the game on breaks with their Aussie colleagues. (Although that story is oft-repeated, scholars aren't so sure about its validity). In any case, the first baseball game in Australian recorded history took place between teams from Collingwood and Richmond. The scores recorded seem a tiny bit on the high side -- 350-230 -- which implies this "baseball" game was probably borrowing more from cricket than the American pastime.
The league flourishes now. They've played in the World Baseball Classic and even won the bronze medal at the Olympics in 2004. They're making quite a name for themselves in the U.S., as well. Over 80 Australian baseball players are in the minor leagues of Major League Baseball, and 28 Aussies have played in the MLB. The league itself is owned by both Major League Baseball and the Australian Baseball Federation, the governing body. The team is placed 11th in the International Baseball Federation rankings.