In no particular order of Greatness:
Dawn of the Dead (1978)
Dawn of the Dead (2004)
Night of the Living Dead (1968)
Night of the Living Dead (1990)
Day of the Dead (1982
The Dead
Zombie
Resident Evil
Resident Evil 3: Extinction
28 Days Later
28 Weeks Later
Zombieland (I hesitate to keep this on the list as it doesn’t exactly fit in zombie horror genre, but it is so good)
Rec
Rec2
Rec3
Rec4
Quarantine
World War Z
and that is all:
I will give honorable mention to: The Beyond, Maze Runner 2, The Girl With All the Gifts, Train to Busan, Return of the Living Dead, The Dead 2, as these are all very enjoyable zombie films, but don’t cut through to be what I consider to be Great.