Q Magazine has polled 50 recording artists, among them Michael Stipe, John Legend and the leader of Travis, to create a list of "Perfect Songs." (Since Leonard Cohen wrote "Hallelujah," they actually mean perfect records).
The winners, in no particular order:

Bitter Sweet Symphony - The Verve
Blowin' In The Wind - Bob Dylan
Born To Run - Bruce Springsteen
God Only Knows - The Beach Boys
Hallelujah - Jeff Buckley
Life On Mars - David Bowie
Perfect Day - Lou Reed
Strange Fruit - Billie Holiday
Strawberry Fields Forever - Beatles
Sympathy For The Devil - Rolling Stones

A few of the indidviduals provide their picks here while Q provides the videos.
Personally, I'll agree with Blowin' In The Wind, Born To Run, God Only Knows and Hallelujah and throw in Marvin Gaye's What's Going On, John Coltrane's Naima, Paul Simon's Graceland, Thelonious Monk's 1947 version of 'Round Midnight, R.E.M.'s Nightswimming, Otis Redding's I've Been Loving You Too Long, NRBQ's Riding in My Car and Junior Murvin's Police and Thieves. Naturally, the list changes depending on the day.