It's too hard to just pick one, because sometimes you feel different about love and you need a different song to represent that.
my favorites:
Return To Me- The last Goodnight.
Sorry- Buckcherry
Feels Like Home- Chantel Kreviazuk
Tonight I Wanna Cry- Keith Urban
Love Remains the Same- Gavin Rossdale
Dreaming With A Broken Heart- John Mayer
Slow Dancing in a Burning Room- John Mayer
Dreaming of You - Selena
3 A.M - Matchbox Twenty
Hero - Enrique Iglesias
Better Than Me - Hinder
And I - Ciara
There are much more... but these are definitely some of the best, for me.