Here's my cocktail hour playlist. I find young and old alike enjoy listening to these classics:

Begin the Beguine
I will wait for you
I'm in the mood for love
Ebb Tide
I wish you love
I've got you under my skin
Fly me to the moon
The way you look tonight
Moonlight Serenade
Never on Sunday
Never can say goodbye / Never Knew Love like this before
Over the Rainbow
Girl from Ipanema
Satin Doll
Misty
Take the "A" Train
Songbird
Europa
Shaker Song
Just the Two of Us

I do not sing on cocktail hours, but I am really a singer and sing most of these songs generally. I play oldies, current stuff, like Jason Mraz I'm yours, etc. but I try to play these standards to keep them alive and in peoples memory.