Review of Delta at DVD Reviewer

Bela Tarr first, whose directorial trademarks are most evident in Delta (and he was mentioned in the credits):

Sátántangó (1994) (many elements of Delta strongly echoes this movie)
A Londoni Férfi (2007)
Kárhozat (1988)
Werckmeister Harmoniak (2000)

Theodoros Angelopoulos:

Trilogia: To Livadi Pou Dakryzei (The Weeping Meadow) (several scenes in Delta remind me of this movie, especially the funereal ambiance of the boat formation sequence; several of Theo's films contain haunting funereal boat sequences, and there are many allusions to people and whole civilizations rising from the water, only to return to the water and vanish)

Mia Aioniotita Kai Mia Mera (Eternity And A Day)
Ulysses' Gaze
Topio Stin Omichli (Landscape In The Mist)

Andrei Tarkovsky - everything. It's the pacing of his films, the photo direction, the camera motion, religious themes, man versus nature themes, humanistic themes, the strongly evocative music

The structure and content of certain scenes in Andrei Rublyov (1966) and Nostalghia (1983) strongly reminded me of Delta. The feeling of the boat dirge in Delta reminded me of the entire feeling of Andrei Rublyov, the religious procession in the early part of Nostalghia, the last few minutes of Nostalghia, the sequence of Pieter Bruegel paintings in Solyaris (1972), an extended driving sequence in Solyaris (1972), the ending leaf scene in Solyaris (1972), a famous moment in Stalker (1979) when the hand is dipped in the water and a burnt out prophecy is spoken which reminds us that man's existence is but an irrelevant blink-of-the-eye moment on the evolutionary scale, so many moments in so many Tarkvosky films, he only gave us seven films so watch them all.

Bruno Dumont - his film Flanders is the inverse of Delta.

Werner Herzog - you mentioned him in your review (Fitzcarraldo). Nearly every film and documentary I've seen of his is excellent, and Delta strongly echoes Herzog's man versus the environment themes, and Herzog's penchant for enigmatic, loopy characters:

Nosferatu: Phantom Der Nacht
Fata Morgana
Lektionen In Finsternis (Lessons Of Darkness)
La Soufrière - Warten Auf Eine Unausweichliche Katastrophe (1977)
Stroszek (1977)
The Enigma Of Kaspar Hauser (1974)
Invincible (2001)
Fitzcarraldo (1982)
Wo Die Grünen Ameisen Träumen (1984)
Herz Aus Glas (1976)
The Great Ecstasy Of Woodcarver Steiner (1974)
Encounters At The End Of The World (2007)
Even Dwarfs Started Small (1970)
Woyzeck (1979)
Glocken Aus Der Tiefe - Glaube Und Aberglaube In Rußland (1995)
Grizzly Man (2005)
The Wild Blue Yonder (2005)
Aguirre, Der Zorn Gottes (1972)
Echoes From A Somber Empire (1990)