Have to agree with JennieG - "so fair art thou, my bonnie lass, so deep in love am I" - I think it's a combo of the words & the melody.
Also - Donal Og is very passionate. LOVE Rod Paterson's versions of Braes O' Balquhidder & Laird O'Drum. (Talk about long-lasting love - they'll be together so long their dust will mingle until indistinguishable.)
Among modern songs, I'm partial to Richard Thompson's "Cooksferry Queen" - "She could make wine out of Thames River water, she could make a believer out of me."
Also, Robbie Robertson's "Broken Arrow," Sting's "Fields of Gold," & Bruce Cockburn's "Sahara Gold" (which is more of-the-moment than everlasting, but still............)
olddude's right too --- probably most of us feel some of the juiciest, most passionate are the ones we've written ourselves...;-)