Microvision has come out with the Nomad Personal Display System, a portable heads-up display that superimposes a virtual 800x600-pixel image on your field of vision. The unit is still kinda bulky and clunky-looking (always a problem with head-mounted displays), but it's getting there. (And the story at Palm Infocenter points out that it's not that great as a PDA screen, given that you can't tap on it, but presumably there'll be portable keyboards that can be used with it, either chording keyboards or forearm-mounted ones.) One interesting aspect of all this is that the unit creates the scan lines essentially by shining a laser into your eye—"Electronics monitor the beam's strength to ensure it will not harm the eye," but I don't know if I trust "electronics" quite that much.
O brave new world, that has such gadgets in't!