Well I also agree, that probably many love songs have already been posted.
I guess a balanced mixture would be alright as well, though I guess, I personally would prefer more modern songs. It is also possible that old love songs are covered by new artists.
Some of those I’d like: (little extract from my Ipod-love-playlist ^^)
Dashboard Confessional feat Juli- Stolen <3
Blink 182- I miss you y3
Elton John- Can you feel the love tonight?
Phil Collins- Can’t stop loving you
Cheap Trick- I want you to want me
Joe Cocker- You’re so beautiful
Foreigner- I want to know what love is
Seal- Kiss from a rose
Seal- Loves divine
Brian Adams- Everything I do (I Do It For You)
Sixpence Non The Richer- Kiss me (!!!! Never found this song, not even at PS-Singstar)
Carpenter- Lovefool
Whitney Houston- I Will Always Love You
Diana Ross & Lionel Richie- Endless Love
Andru Donals- All out of love
Heart- All I want to do is make love to you
alicia Keys- Fallin’
Bonnie Raitt- I can’t make you love me
U2- With or without you
Michael Bublé- Cuando cuando cuano
Michael Bublé- Everything
Michael Bublé- Fever
James Morrison- You give me something
Ten Sharp- You
Lifehouse- You and me
Oasis- Wonderwall
Gavin Rossdale- Love remains the same
German tracks:
Echt- Weinst du
Xavier Naidoo- Ich kenne nichts
Silbermond- Das Beste
Freundeskreis- Mit dir
Herbert Grönemeyer- Ich hab dich lieb
Sportfreunde Stiller- Ein Kompliment
Sportfreunde Stiller- Lass mich nie mehr los
Lena-Meyer-Landrut- Satellite
Perhaps, it chould be checked, that the tracklist isn’t going to be all too… let’s say trashy or sad. Men should also want to sing those songs I suppose. 
So put some alternatives at the ready:
Kiss- I was made for loving you for instance
Jan wayne- Only you
David Guetta- Gettin over you…
Rooney- when did your heart go missing