As for ones that didn't make the cut for me...
Firstly a few very obvious ones, discounted because they were too obvious
The First Time Ever I Saw Your Face – Ewan MacColl or Roberta Flack
(I could happily make a case for this being the greatest love song ever written)
The Beach Boys – God Only Knows
(The other record I could happily make a case for being the greatest love song ever written)
Echo and The Bunnymen – The Killing Moon
(Got a brilliantly romantic vibe to it)
Otis Redding – pretty much everything he ever recorded
(thought about nominating Tramp as an example of when love is less than smooth)
Death Cab For Cutie - I will Follow You Into The Dark
(I like love songs with a bit of existential angst in them)
A few (maybe) less obvious ones that crossed my mind..
Vic Chesnut – Flirted With You All My Life
(Not a love song at all but sort of is. Subverts the use of a ‘love song’ for other purposes)
The Black Keys – Tighten Up
(If it’s a blusey love song it’s got to have the word “ache” in there – them’s the rules)
Nick Cave / PJ Jarvey – Henry Lee
(By definition most murder ballads are love songs)
Dar Williams – The One Who Knows
(Somewhat impressively written by someone who at the time didn’t have children of her own)
Big Mama Thornton – Hound Dog
(How that song is supposed to sound - again when love breaks down)
Loads of others but we'd be here all week!