But as the lady stated, it all depends on what the lady likes...
What might be a killer song for one might be a total turn-off for the other.
As for good all-round songs that sound good on an acoustic guitar you can allways relly on 80's soft rock. If you require more specifics you can stick to The Police/Sting, U2, REO Speedwagon's "I can't fight this feeling", The Bangles' "Eternal Flame", Boston's "Amanda". Bryan Adams has several "killer" songs like "Everything I do", "Heaven", "Have you ever loved a woman", "Let's make a night to remember", "Please Forgive me", etc.
On a personal note, some hand picked piano songs might get the desired result as well, have any of you tried "A Kiss to Build a Dream On" by Louis Armstrong? Simple and sweet, and you might just get what the song is asking for...