Tomorrow Never Knows
Above is a great piece on how The Beatles took ideas from avantgarde composers into the pop charts. For further reading on this I recommend Craig Schuftan's The Culture Club because he charts the influences widely and comes to some really disturbing conclusions about pop music.
Various sources on the internet have mentioned the amount of money paid by producers of the show Mad Men to use the track in a recent episode and, it seems to me the producers had no choice. Sure, it'd be a bit weird to see Don Draper say something about The Beatles and not hear them but could anyone make a convincing reproduction of this tune, with all the tape loops and effects?
More to the point, what other song captures the zeitgeist of the time? Within a couple of years The Beatles were transformed by their use of drugs and thousands followed them on similar trips into their own self-consciouses.
One of my favourite tracks to reference The Beatles' Tomorrow Never Knows is The Chemical Brothers' Setting Sun. I like how the clip represents the idea of finding yourself by taking psychedelic drugs but in the '90s it was MDMA rather than LSD, which had become difficult to source for a new generation of astronauts exploring inner spaces.