Jacques Tati's Playtime -- absolutely. great call.
Roma: La Citta Aperta. Underrated in US, not in Europe.
Speaking of Mizoguchi, I nominate those and virtually every film by Ozu. Esp Tokyo Story and Green Tea with Rice
Underrated Kurasawa films: Ikiru, High and Low, Dodes ka'Den, and Dersu Uzala
In fundamental ways almost all Coen Brothers movies are underrated EXCEPT Fargo which got the praise it deserved and Big Lebowski which has become an acknowledged classic. All the rest are underrated as far as I'm concerned. After Scorsese and Mallick these guys are the finest American filmmakers of our time.
Speaking of Mallick: Badlands
Speaking of Scorsese: King of Comedy
indie films that no one much knows about:
TV with what'shisname the sex addict from X Files
Charlotte Sometimes
Eros
Full Frontal
Wong Kar Wai films, ESPECIALLY In the Mood for Love
Lust, Caution by Ang Lee
Into the Wild by Sean Penn
The second Tarzan movie, (Tarzan Takes aWife? something like that...)
The Jacket
Inglorious *******s
Friiends of Eddie Coyle
Three giant movies from the late 60s and 1970s that are way way better than you even remember them being: Midnight Cowboy, Chinatown, and Taxi Driver
Ditto for 1990s: Glen Garry Glen Ross and Fight Club
Advise and Consent (Otto Preminger)
Almost all of Godard's films other than Breathless. Esp A Gang Apart and La Chinoise
Knife in the Water (Polanski)
Battle of Algiers (amazing)
Shoah (seen in 1 sitting esp)
Berlin Alexanderplatz (seen in two sittings esp)
and so many many more.....