pretty much all of them...i sometimes feel very hollow when i'm skipping songs on spotify that i have curated and love, but have heard enough times that i kind of don't need to hear them anymore.
the most significant song i feel like i ever heard was 'wuthering heights' by the incomparable kate bush. it was on our local community radio in the car, i didn't actually even get to find out what it was or who it was cause the dj never said. i was beautifully haunted until like two weeks later when i heard it again on the radio and they actually identified the song- i was about 14, we were taking my little brother to a karate lesson - and i just felt like no other music i had known up to then really mattered anymore. i had been a little metal head and was just obsessed with guitars - then i was like, holy shit, i need to hear all of her music and need to play piano/keyboards as well as guitar and also any other instrument i can get a sound out of. my whole musical interest shifted and i feel like my emotional self developed a lot too - it was a hell of an experience.
edit: hearing all of prince's music was obviously very full on too, but kate led me to prince. hearing the first roxy music album was also a very incredible experience, very, very, very!