DC3-first real airliner where you stood a good chance of getting to your destination alive, brought the notion of air travel to the world. Plus it did a bit in the war etc. I remember the last RAF DC 3 retiring, it would have been around 1968.
P51- the best fighter of WWII. Took the escort task all the way to Berlin and was a game changer.
Gloster E28/39-I know the Germans got there first but this was the real start of the jet era, leading to the
Comet-world beater; if only they had thought about those square windows a little more.
C-130-Ford Transit of the air.
747-mass world transport, still going strong 45 years later.
Cessna 172-more 172's have been built than any other aircraft, some 43,000 to date since 1956. What most pilots including me would have learned to fly in. Apart from the 182 probably the best all round light aircraft ever built.