Well I guess these are pretty obvious but anyway...
Friday the 13th includes many scenes copied from Mario Bava's
Reazione a Catena (the impaled couple, for example). The whole movie can be considered an unofficial remake.
Norman J. Warren saw
Suspiria 1000 time before directing
Terror. Just watch the trailer here :
http://fr.youtube.com/watch?v=mLMuHjEV-RM
A shameless rip-off!
Many movies were (indirectly) inspired by Mario Bava's "the telephone" story in
Tre Volti Della Paura/Black Sabbath.
When a Stranger Calls by Fred Walton is probably the first.
Carpenter's
Halloween is a direct homage to Dario Argento and Sergio Martino (especially
Torso,
The Bird with Crystal Plumage and
Deep Red). The masked killer, the big knife, the music, the pace, the killer POV, etc...
Brian De Palma's
Dressed to Kill has a bit of L'
Uomo Senza Memoria in it (Angie Dickinson is wounded the same way as Senta Berger, with exactly the same camera angle). Italian film makers were a huge influence on Brian De Palma...
Stanley Kubrick stealing ideas from Sergio Martino? Maybe... In one sequence of
Your Vice is a Locked Room..., a writter, violent and schizophrenic, keeps typing the same sentence over and over. I saw something similar in
Shining ;-)
Pascal Laugier's
Saint Ange is a gore-less melodramatic variation on Lucio Fulci's
The Beyond and
The House by the Cemetery. The ending is 100% Fulci: Virginie Ledoyen, here eyes totally white, trapped in a "death zone"...
Eli Roth is a fan of Aldo Lado. We all know it. In
Hostel II, he wanted to make a sequence similar to
The Night Train Murder (isolated young girls in a train, victim of deranged junkies). But he failed completely! An ultra modern train that includes a night club full of teenagers is not scary, just silly.
Richard Marquand's
The Legacy is, for me, a modern version of Mario Bava's
Lisa e il Diavolo.
In one sequence of
King Kong, Peter Jackson enters in Italian territory. When we discover the tribe on the Skull island, I felt I was in an Umberto Lenzi cannibal movie!
OK that's all for today...