Found this cool Harley Quinn playlist on Tumblr.  It consists of:

Bad Girl – Avril Lavigne feat. Marilyn Manson

Madhouse – Little Mix

My Leftovers – Porcelain Black

Pretty Little Psycho – Porcelain Black

Kinda Outta Luck – Lana Del Rey

Do It Like A Dude – Jessie J

Bubblegum Bitch – Marina and the Diamonds

Mad Hatter – Melanie Martinez