Vocals are sung by guest artists including Jette von Roth, Kêta Jo McCue, Cristina Scabbia, of Lacuna Coil, Sheppard Solomon, Samu Haber of Sunrise Avenue, Sarah Brightman, Moya Brennan of Clannad, Adam Young of Owl City, Andrea Corr of The Corrs, Colbie Caillat, Sarah Howells of Welsh emotional folk / indie band Paper Aeroplanes, Ben Becker, Peter Heppner of synthpop band Wolfsheim, MiLù – also known as Mila Mar, Xavier Naidoo, Arlissa, Maya Saban, Kim Sanders formerly of Culture Beat, Ana Torroja of the Spanish pop group Mecano, Tarja Turunen formerly of power metal group Nightwish, Despina Vandi, Alexander Veljanov of Darkwave group Deine Lakaien, Swedish singer September, French voice artist Pierre Maubouch
