The US Airways jet that crashed into the Hudson was equipped with a special device unique to Airbus planes that increased the likelihood it would stay on top of the water.The "ditching switch" closes all the valves and ventilation ports on the fuselage. Because airplanes are pressurized, they are capable of floating for prolonged periods of time, as long as they don't break up when they hit the water.
And here's a makes-sense-when-you-think-about-it fact: "when they're full of fuel, which is lighter than water, they will float, as long as their structural integrity is intact."
The Airbus A-320, along with the Boeing 737-800, is one of the two most ubiquitous aircraft in American air travel. It is "as garden variety as airplanes get."