There was a brief period of competition in the late 70s / 80s when Airbus and Lockheed were trying to be different. Order was soon restored, then came the 90s with the regional jet fad and the rise of Embraer and Bombardier.
But now we're back to a big duopoly. Ilyushin are still around but only Cuba still buys from them. The next shake-up will come from China; once their civil aviation designs reach the sophistication of their military aircraft they'll start earning orders across Asia, then Europe..