These are the best places to start. Usually they are the most accessible/entertaining/American. Sometimes they are just one of their shortest (if you're going to end up not liking a director, better to only waste 90 minutes rather than 200).

Enjoy your quest...

FELLINI: I Vitelloni

BERGMAN: Wild Strawberries

GODARD: Breathless

TRUFFAUT: 400 Blows

DREYER: Passion of Joan of Arc

RENOIR: The Grand Illusion

ROSSELLINI: Flowers of St. Francis

OZU: Late Spring

KUROSAWA: Seven Samurai

BUNUEL: Los Olvidados

VISCONTI: Notti Bianche

MIZOGUCHI: Ugetsu

ANTONIONI: The Passenger

OLMI: Il Posto

TARKOVSKY: Andrei Rublev

BERTOLUCCI: The Conformist

PASOLINI: Gospel According to St. Matthew

HERZOG: Aguirre, the Wrath of God

KIAROSTAMI: Taste of Cherry

YIMOU: Raise the Red Lantern

HOU: Three Times