There are a few 21st century films in my top 100:
Crouching Tiger, Hidden Dragon
Kill Bill, volumes 1 & 2
Lord of the Rings: The Fellowship of the Ring
Mad Max: Fury Road
That's just off the top of my head, there may or may not be more.
I don't judge movies on pop-culture relevance or box-office take, though. I judge them on story and aesthetics, and technical difficulty where applicable.
I think pop culture relevance is important, imo. A film is so popular it becomes part of our everyday life. It's remembered.