This is a link to a CD which discusses the effects of various types of music. No effort is made to legalize what should be listened to; the speaker just addresses some studies that have been done. You will make your own conclusions, I assure you.
It is fascinating, especially the studies that find mice killing each other when listening to certain rock groups but successfully navigating complex mazes when listening to Mozart!
Produced by an educator who teaches and sells a writing program we use (Andrew Pudewa, IEW, www.writing-edu.com) it provides evidence that the type of musical input we provide will have an effect on our children's development.
I highly recommend this CD set.