I used to always have my mp3 player going when training, listening to pop rock at the lightest and screamo metal at the heaviest. I don't consciously listen to anything while doing strength training nowadays, though, because focusing on a song that I'm into means not focusing on my lifting and vice versa. So now my playlist for most of my training is whatever bland music is playing in the public gym. If I'm doing cardio, though, I might revert back to pop rock and screamo.