Deep Red: While this wasn't Argento's final giallo it remains the point to which he took the still youthful crime genre to heights of design and plot contrivance clearly indicated by the originals by Bava et al in the 60s. It's a kind of apotheosis. David Hemmings plays a British composer working in Rome who witnesses a horrific murder and runs to the crime scene. He is too late but he is committed to solving the crime. Teaming up with crime journalist played by Daria Niccolodi he goes on an ever more intriguing journey into mystery. A mix of Elizabethan invention (I can only think of one case in an Argento movie in which someone is killed with a bullet; mostly its blades or glass shards or whatever you don't want to see lying around the house used fatally) and high baroque style with the lights off, Deep Red is a masterpiece.
Eraserhead: Worlds from daydreams are often pleasant places and those created in attempts to mask the real life fears of their protagonists characteristically involve a redemption narrative arc. Until Eraserhead you had to go to someone like Tarkovsky or Jodorowski for alternatives to this, individualist auteurs from the DNA up. With Eraserhead this lonely stage had one more figure and appropriately he, like they, didn't look like any of the others.