We looked at Naturespace Holographic Audio back in May of 2009. I liked it then, and I like it more now. Naturespace is a free iPhone app that plays back carefully recorded natural environments designed for listening on headphones.
The recordings are created using the binaural technique, where two closely spaced microphones approximate the distance between your ears. When you put headphones on, the results can be dramatic and hyper-realistic.
The free app has no ads, and comes with six audio environments which are very relaxing and can simply transport you to another place. With good headphones (I use the
