“Unchained Melody” always makes me think of the movie Ghost.
“One tin soldier” by COVEN from the movie “Billy Jack”
“Surfin’ Bird”—Full Metal Jacket
And was Queen’s “Who Wants to Live Forever” written just for Highlander?
“In Dreams”–Blue Velvet when Dean Stockwell sings in the living room and later when Dennis Hopper and his goons beat up Kyle McClachlan.
“Old Time Rock n’Roll”–Risky Business during Tom Cruise’s much parodied underwear dancing scene.
This is probably just me, but I can’t listen to Jefferson Airplane’s “White Rabbit” without thinking of the scene in
The Game where Michael Douglas comes home to find that his house has been totally f*cked up.
“Sweet Jane” forever reminds me of Natural Born Killers–the damn song is played throughout the entire movie.
Whenever I hear the piano riff in “Layla,” it reminds me of the scene in Goodfellas where all those people start turning up dead.
Everybody’s Talkin’ by Nilsson can not be listened to without thinking of Midnight Cowboy
Also, from the same movie, I now associate Donovan’s “Atlantis” with Pesci’s and DeNiro’s characters viciously beating up Billy Bats in the bar.
“The Entertainer” from The Sting.
And how can this thread be so long with no mention of ** The Graduate**? “And here’s to you, Mrs. Robinson” was written before the film.
“Dueling Banjos” brings Deliverance to mind, and “Goodnight Sweetheart” reminds me of American Graffiti.
Saw ‘Love Actually’ last night - it has a brilliant use of Joni Mitchell’s recent version of ‘Both Sides Now’
‘Ain’t Too Proud to Beg’ in The Big Chill
‘Pinhead’ by the Ramones in Freaks - the song wouldn’t be written for another 45 years! Yet they knew the words! That is freaky.
“What condition my condition was in” will always summon visions of leggy nordic blondes and bowling balls to my mind. Don’t ask why.
“The Glory of Love”–Karate Kid II (unless it was written for the movie…)
That god damned Dion song and that god damned boat movie.
One Vision by Queen (Iron Eagle)
Who Wants to Live Forever by Queen (Highlander)
Secret Garden by Bruce Springstein (Jerry Maguire)
Don’t Want to Miss A Thing by Aerosmith (Armageddon)
These are television and don’t really count, but…
In the Air Tonite by Phil Collins (Miami Vice)
You Belong to the City by Glenn Frey (Miami Vice)
Smuggler’s Blues by Glenn Frey (Miami Vice)
Day-O (Harry Belafonte) in Beetlejuice
Kokomo (Beach Boys) in Cocktail
If You Leave (OMD) in Pretty In Pink
I Melt With You (Modern English) in Valley Girl
Bad to the Bone (George Thorogood) in Christine
Blue Moon (various versions) in An American Werewolf in London
Oh Yeah (Yello), Twist and Shout (Beatles), and Danke Shoen (Wayne Newton) in Ferris Bueller’s Day Off
When I’m 64 (Beatles) in The World According to Garp
“Somewhere Over the Rainbow” by Judy Garland in Wizard of Oz & The Abominable Dr. Phibes (starring Vincent Price)
“Here Comes Santa Claus Right down Santa Claus Lane” played during the SWAT invasion scene in National Lampoon’s Christmas Vacation starring Chevy Chase
“My Sharona” by the Knack during the Circle K gas station dance scene in Reality Bites
“Stay” by Lisa Loeb from the credits titletrack for Reality Bites
“Somewhere Out There” sung by Linda Ronstadt & James Ingram in An American Tail
“You’re Where I belong” sung by Trisha Yearwood in Stuart Little
48 hrs…Roxanne…sung by Eddie Murphy.
That’s precisely what I was going to say! It’s…um…Celine someone and it goes…I dunno, but she hit those high notes as the boat went down, the band played on, and he sank beneath the icy water …sob…
No, really, I’m OK.
That one is tops. Everyone I knew calls it “the banjo tune from Deliverance”.
Of course, the Celine Dion song was written for Titanic so it doesn’t fit the OP. Not that that matters. 
My vote: The second movement to Mozarts 21st Piano Concerto (in C), now known as “Elvira Madigan” after the movie in which it was featured.
“Ode to Joy” and A Clockwork Orange.