I'll comment more extensively (in general and also on my own list) when I'm back, meanwhile, here's my list (I'll fix the formatting later): 


Hamlet (Sven Gade, Heinz Schall, 1921) 
Die freudlose Gasse  The Joyless Street (Georg Wilhem Pabst, 1925) 
M - Eine Stadt sucht einen Mörder  M - A City Is Looking For A Murderer (Fritz Lang, 1931) 
Zu neuen Ufern  To New Shores (Detlef Sierck [= Douglas Sirk], 1937) 
Liebe '47  Love '47 (Wolfgang Liebeneiner, 1948) 
Der Verlorene  The Lost One (Peter Lorre, 1951) 
Das fliegende Klassenzimmer  The Flying Classroom (Kurt Hoffmann, 1954) 
Monpti (Helmut Käutner, 1957) 
Die toten Augen von London  The Dark Eyes of London (Alfred Vohrer, 1961) 
Der Schatz im Silbersee  The Treasure of Silver Lake (Harald Reinl, 1962) 
Die endlose Nacht  The Endless Night (Will Tremper, 1963) 
Die Tote von Beverly Hills  The Dead Woman of Beverly Hills (Michael Pfleghar, 1964) 
Abschied  Farewell (Egon Günther, 1968) 
Sieben Tage Frist  Seven Days of Grace (Alfred Vohrer, 1969) 
Götter der Pest  Gods of the Plague (Rainer Werner Fassbinder, 1970) 
Rote Sonne  Red Sun (Rudolf Thome, 1970) 
Deadlock (Roland Klick, 1970) 
Ich liebe dich, ich töte dich  I Love You, I Kill You (Uwe Brandner, 1971) 
Faustrecht der Freiheit  Fist Right of Freedom (Rainer Werner Fassbinder, 1974) 
Das Ende des Regenbogens  The End of the Rainbow (Uwe Frießner, 1979) 
Alpha City (Eckhart Schmidt, 1985) 
Schramm (Jörg Buttgereit, 1993) 
Die tödliche Maria  Deadly Maria (Tom Tykwer, 1993) 
Requiem (Hans-Christian Schmid, 2006) 
Auf der anderen Seite  The Edge of Heaven (Fatih Akin, 2007) 

I would've loved to expand it to 30 or 35 films but I wasn't sure if that's okay, so I tried to limit it to 25. 
As usual, I didn't order the films by my personal appreciation but by the years they were produced. 
Furthermore, though this is a very personal list, I tried to include at least two films from every decade, that's why the two latest efforts are in (they also are personal favourites nevertheless).