Ambassador, Buick, Chrysler, Dodge, Mercury, Oldsmobile and Rambler all offered 4 door pillarless wagons in the late fifties, early sixties, but Mercury was the only manufacturer to offer a 2 door hardtop wagon.
The Chevrolet Nomad and Pontiac Safari are not counted, as they were not officially pillarless wagons.
As you say, Mercury 2 door wagons look great and were only produced for three years. This body style was deleted for 1960. The above picture is a 1959 model, the last of this body style.