I debated my top spot between A Hard Day's Night and Spinal Tap. Tap is a great movie as well, but Night edged out because of its iconic documentation of history in the making.
Metaldams, look at the film again. It's so much more than screaming girls chasing The Beatles. Sans the opening sequence and the performance footage, there is great word play, stylish directing, clever writing and lots of mad cap scenes. It's the closest thing to a rock music Marx Brothers movie as you're liable to find. The bit with the English businessman putting down the younger generation with Lennon putting the soda bottle to his nose and sniffing it (wink-sniffing coke even though it was Pepsi), the shaving scene, the football field scene, the casino scene,and many other great things. Watch it again! Ebert calls it the Citizen Kane of Jukebox movies and plenty of critics cite it as the top rock movie, and I agree. And, yes, with other groups, it wouldn't have had the magic. It was the charm of The Beatles, the clever writing and Dick Lester's stylish directing that made it what it is. That's the point! Put two other actors in Casablanca and the results would differ as well.
I debated Jailhouse Rock, as it is corny by today's standards and doesn't hold up as well as the others I listed, but it is an iconic movie, and Elvis' best next to Viva Las Vegas, which is no Hard Day's Night, either. I was going to put Rock and Roll High School in with The Ramones, as it was the last real classic authentic drive-in movie, but iconically, Jailhouse beats it!