"The Princess Bride" (Mark Knopfler) theme -- essentially a love theme, I would say.
So shoot me ... but the way they used the Don Peake arranged instrumental of the song "White Bird" for Michael's love theme in one (or two) episodes of "Knight Rider", was highly affective if you ask me.
The love theme and variations in Henry Mancini's "The Thorn Birds" -- a fantastic 2CD set from Varese that has shockingly not sold out. A MUST have, if you ask me. I couldn't find a good version of it, but here is a clip from the film with it playing:
http://www.youtube.com/watch?v=iPF2v7vd ... re=related
"Rose" from "Titanic", is seconded. The deeply haunting version that leads into the ice berg appearence, ... just not something one forgets.
The Buffy/Angel love theme from season 2 (though still used on occassion afterward) of "Buffy the Vampire Slayer" (Christophe Beck):
http://www.youtube.com/watch?v=63PDuiZAxjU
"Spaceballs" love theme (John Morris).
Could "Dana's Theme" from "Ghostbusters" count?
Is Molly's theme from "Ghost" a love theme?