Paul: Happy Together by The Turtles,
Because whenever you are with him, you are always happy.

John: What A Wonderful World by Louis Armstrong, because whenever you're with John, you always feel like the luckiest girl in the world.

George: Brown Eyed Girl by Van Morrison, because George loves making you laugh so he could see your eyes light up and sparkle.

Ringo: Stand By Me by Ben E. King, because whenever Ringo is feeling down, you are always standing by his side whenever he needs you.

- @Sunshinemccartney