Canada will hold a parliamentary election on October 19, 2015. Polls suggest that the New Democratic Party is in a virtual tie with the Conservative Party, with the Liberals trailing badly. For most of its life, the New Democratic Party has been a strong party but not one of the two largest parties. There seems to be a possibility that the NDP will form the next Canadian government. See this story.
This is an example of how party systems can bring new parties into power. Canada does not have proportional representation but it does have equal and tolerant ballot access.