A good site I've found for music playlists is
http://www.inthegym.net/ - they have music by genre and the type of workout.
The music on my MP3 is a mix of Kanye West, Nelly Furtado, The Killers, Justin Timberlake, The Ting Tings, Britney Spears, Gwen Stefani, Madonna, Flo rida, Jay z, Lady Gaga ... and that's all I can think off off the top of my head.