The following films are considered public domain in the US (the copyright protection has lapsed) and can be downloaded, sold and exhibited by anyone. 

The Driller Killer

Lady Frankenstein

Night of the Living Dead (1968)

The Satanic Rites of Dracula

Horror Express

Drive-In Massacre

Sisters of Death

Messiah of Evil

Nightmare Castle

Incredible Two-Headed Transplant

Mutant (1984)

Grave of the Vampire

Savage Weekend

Silent Night, Bloody Night

Don’t Look In The Basement

Haxan: Witchcraft Through The Ages

Bride of the Monster

Glen or Glenda

Plan 9 From Outer Space

Beast of Yucca Flats

Dominique (aka Dominique is Dead)

Scream Bloody Murder

Reefer Madness

Marihuana

Cocaine Fiends

Assassin of Youth

Carnival of Souls

Last Man On Earth

The Trial (1962)

A Bucket of Blood

Phantom of the Opera (1925)

The Cabinet of Dr. Caligari

M (1931)

Nosferatu (1922)

Embryo

Little Shop Of Horrors (1960)

Dementia 13

The Terror

Freaks

Bloody Pit of Horror

Atom Age Vampire

Death Rides A Horse

The Battle of El Alamein

Horror Hotel

White Zombie

A Trip To The Moon

The Hunchback of Notre Dame (1923)

Bruce Lee Fights Back From the Grave

Images of Bruce Lee

Black Fist

The Street Fighter (1974)

Return of the Street Fighter

The Street Fighter’s Last Revenge

The Real Bruce Lee

Battleship Potempkin

Blood Tide

Eegah

Faust (1926)

Greed (1924)

Jail Bait

The Violent Years

Metropolis (1927)

Planet of Dinosaurs

Spider Baby

Mad Dog Morgan

Frankenstein’s Castle of Freaks

Frankenstein ‘80