Well, of course everything is a matter of taste and it depends what your video store + libraries have in, so i'll suggest a range, a mix of old + new, critical + popular favourites.

Sansho the Bailiff (Mizoguchi, 1954) +/or Ugetsu Monogatari (Mizoguchi, 1953)
Tokyo Story (Ozu, 1953)
Andrei Rublev (Tarkovsky, 1966)- slow + long (it's no Run Lola Run) but worth giving a try. 
Crouching Tiger Hidden Dragon (Ang Lee, 2000)
City of God (Meirelles, 2002)
L'Atalante (Vigo, 1934)- make your own mind up; wpqx and i have had very different reactions.
Cinema Paradiso (Tornatore, 1989)
My Neighbour Totoro (Miyazaki, 1988) +/or Spirited Away (Miyazaki, 2001)
The Green Ray (Rohmer, 1986)
Zatoichi (Kitano, 2003)
Central Station (Salles, 1998) 
Grand Illusion (Renoir, 1937) +/or Rules of the Game (Renoir, 1939)
Aguirre Wrath of God (Herzog, 1972)
Twilight Samurai (Yamada, 2003)
Pather Panchali (Ray, 1955)
Metropolis (Lang, 1927) +/or M (Lang, 1931)
Oldboy (Park Chan-Wook, 2003) not for the squeamish
Talk to Her (Almodovar, 2002)
Rashomon (Kurosawa, 1951)
The Discreet Charm of the Bourgeoisie (Bunuel, 1972) +/or Belle de Jour (Bunuel, 1967)
Battleship Potemkin (Eisenstein, 1925)
Jean de Florette/Manon des Sources (Berri, 1986)
Amelie (Jeunet, 2001)
The Double Life of Veronique (Kieslowski, 1991)
Raise the Red Lantern (Zhang Yimou, 1991) +/or House of the Flying Daggers (Zhang Yimou, 2004)
Children of Paradise (Carne, 1945)
Fanny and Alexander (Bergman, 1982) +/or Persona (Bergman, 1966) +/or The Seventh Seal (Bergman, 1957)
Night of the Shooting Stars (Taviani bros, 1981)
Bicycle Thieves (De Sica, 1948) 
Pierrot le Fou (Godard, 1965) +/or Breathless (Godard, 1960)
The Leopard (Visconti, 1963)
The 400 Blows (Truffaut, 1959)
A Man Escaped (Bresson, 1957)
The Passion of Joan of Arc (Dreyer, 1928) 

my personal favourite is Sansho the Bailiff.