It's impossible to say but I've always thought 'I Saw The Light' by Todd Rudgren to be as close to a perfect pop song as you will ever hear.

MacArthur Park, written by Jimmy Webb

This is my fave of anything mentioned in this thread so far.

I knew my official top 10 but shall come off the fence and commit to a song I got to know aged 21, although it was quite a few years old by then. It has, perhaps uniquely, never been less than one of my all-time fave songs: the Beach Boys with Do It Again. http://www.youtube.com/watch?v=XHpjILzv1P4

The Edge of Glory - Lady Gaga

Also big shoutouts to:

It's My Life - Bon Jovi
Backstreets/Born To Run/Thunder Road - Bruce Springsteen
Take Me Along - Miley Cyrus (don't laugh, it's an incredible song!)

Very difficult to compare across genres but this would make my shortlist:

DOWN IN THE PARK - Tubeway Army

Few of mine.

Bjork - Venus as a boy
Bob Marley - Is This Love
Elvin Bishop - Fooled Around And Fell In Love
Herb Alpert - This Guy's in love with you
Badly Drawn Boy - Once Around the block
Echo and the Bunnymen - The Killing Moon
INXS - Mystify
Joy Division - Love Will Tear Us Apart.

& many, many more.

Don't stop me now - Queen

Come on Eileen!

Enjoy The Silence - Depeche Mode
Over My Shoulder - Mike & The Mechanics