You can't make a list of great zombie/horror films without including Night of the Living Dead - it's truly a groundbreaking film that laid the groundwork for countless other films of this genre.

However, I find it fascinating that the film that inspired George Romero to become a filmmaker was not another horror film or even any of the Universal Monster movies... But a filmed version of the Offenbach opera, The Tales of Hoffmann. Sometimes inspiration comes from unlikely sources.