I love this free sampler compilation, but I must admit that not all the tracks are set at the same volume level, which is a bit of a pain. These tracks are really great to get going with, and will appeal to loads of people.
Personally I got into heavy metal when I used to do shift work, and it is great to wake you up first thing in the morning. Over the years since then though, loads of people have told me that they love this type of music to de-stress by. Ideal as this is free to download and listen to.