These are good suggestions for planning a music workout, and I use this method, myself. If you want music you can really push your workout with, think about the songs that make you turn the radio up full blast and sing at the top of your lungs. Chances are, having that song in your workout mix will give you a great boost of energy when you need it.
A friend of mine says a must have in his mix is "The Immigrant Song" by Led Zeppelin. One of my favorites is "Hold Back the Rain," by Duran Duran. But use whatever works best to get you moving.