hmd [the libarynth]

head mounted displays

from 25 USD http://jakeofalltrades.wordpress.com/2007/09/30/25-head-mounted-display/#more-112
or 250 USD http://www.i4u.com/article4612.html
eMagin http://www.vrlogic.com/html/emagin.html
Various http://www.yellomosquito.com/
Comparison http://www.stereo3d.com/hmd.htm#chart

eye mounted displays

http://www.eurekalert.org/pub_releases/2008-01/uow-clw011708.php

useful for mixed reality or virtual reality applications