Java applet of Demonstration for Head Related Transfer Function.
Please listen with headphones.

Refferences:
[1] T. Nishino, S. Kajita, K. Takeda, F. Itakura, "Interpolation of head related transfer functions of azimuth and elevation," The Journal of the Acoustical Society of Japan, 57(11), pp.685-692, 2001
[2] http://www.sp.m.is.nagoya-u.ac.jp/HRTF/
[3] http://en.wikipedia.org/wiki/Head-related_transfer_function