What music should you listen to when you are exercising?

Whatever you like. Any music that you enjoy, that gets you motivated, and that maintains your focus and interest is just fine. If you like dance, techno, house, electronic, dubstep, that's great. But if you like country or pop, that's equally fine as well. There's no "proper" music to listen to. Some people even listen to audiobooks when exercising - no music there!