The Wassily Chair by Marcel Breuer. Designed in leather and tubular steel in 1925. One of THE classic chairs I think this chair look best on its own or in a pair.
This is the LC2 chair by Le Corbusier, Pierre Jeanneret and Charlotte Perriand in 1928. Originally made by Thonet it has had many reinventions as you can see below.
This is the Barcelona chair by Mies van der Rohe. Used in homes and commercial interiors, in modern and classic settings it is the chair all designers use give a stylist look. It was designed for the Barcelona Pavillion Mies van der Rohe created for the Barcelona Exhibition in 1925. I personally like it in classic white. I think black looks bit clinical.