What do we mean by greatest? So many to choose from. It's so easy to pick a John Williams love theme (BTW, I would consider Princess Leia's theme a "Love Theme".) but there are many from the Golden and Silver age as well. How about Romeo and Juliet by Nino Rota?
I'm probably more obscure in my choices here, but a few that first pop in my mind:
- The love theme from Witchfinder General by Paul Ferris - Across the Stars by John Williams - Love theme from Waxwork by Roger Bellon Last but not least - Love theme from Dan Curtis' Dracula by Robert Cobert
I would say Vertigo is the greatest, with Cinema Paradiso being my personal choice.
Another vote for Vertigo
Almost impossible to name one (though surely it will be one by John Barry! ) but on hearing the Joel McNeely/RSNO 1996 recording of this classic Bernard Herrmann score a few days ago I couldn't help thinking the gorgeous love theme is styled very much on Richard Wagner's Tristan und Isolde: Liebestod ...
It doesn't get much better than this for me (Love Theme from Superman)
Kev, you have no idea how much my better half detests that song. She groans whenever an instrumental version plays but the Margot Kidder recital is a definite no-no! Mitch
So many to choose from. It's so easy to pick a John Williams love theme (BTW, I would consider Princess Leia's theme a "Love Theme".) but there are many from the Golden and Silver age as well. How about Romeo and Juliet by Nino Rota? 
) but on hearing the Joel McNeely/RSNO 1996 recording of this classic Bernard Herrmann score a few days ago I couldn't help thinking the gorgeous love theme is styled very much on Richard Wagner's Tristan und Isolde: Liebestod ...