To quote my ex boyfriend "every mix for a girl requires one Billie Holiday song."
that's pretty much true. or Louis Armstrong. Billie or Louis. i would recommend "La Vie un Rose" by Louis Armstrong.
also:
Light Up My Room - Barenaked Ladies
I'll Be Your Man - The Black Keys
Stickshifts and Safetybelts - Cake
Lips like Sugar - Echo and the Bunnymen
When U Love Somebody - Fruit Bats (yes, i know it uses U instead of You, but it's still good)
I Walk the Line - Johnny Cash (or there's a cover of it sung by a girl, but i don't know who it is.)
Soundtrack for Our Movie - Mae
Run - Snow Patrol
Apple Blossom - The White Stripes