Not the "best" movies to go on like an AFI list, but the ones that shaped me:
Blue Velvet - my first (only?) exposure to that level of mordant humor and Freudian menace
American Movie - I watch this at least once a year and feel its rawness and sadness a little more profoundly each time
Gummo - my people, finally represented on screen
Zodiac - captures something no one talks about, which is how fucking *dark* the Bay Area is. A procedural, but less about cops and more about a kind of media terrorism and the propagation of social-psychological contagion
Twin Peaks: FWWM - the first 30 minutes rewired me permanently, never been the same since
Raising Arizona - I grew up in the sticks and this was the first "art film" I ever saw. Watched it enough times to memorize every line