I think this can be answered both generally, and specifically. Any music that is soothing is wonderful. And the scientific advancements they are making in this area is just phenomenal. Yes, you read that right. They have tuned into the fact (ha ha, see what I did there!) that certain tones and frequencies elicit certain responses, and can now write the music specifically for that purpose. I think that is so cool! An example is music that includes delta waves to help encourage you to sleep.
So, when I am working on someone, I use a collection I found on iTunes called Serenity, Spa Music 101 and it contains 101 selections. Some of it’s pieces are scientifically designed, if you will.
When I am on the table, my therapist uses a CD collection called Solitudes, Relaxing Naturally which I really like as well. It has many animal sounds in it that are just amazing.