Consumer partially transparent head mounted displays are sort of available. SiliconMicroDisplay has one that is bulky and not really transparent enough to walk around in, but could be used to approximate Project Glass: http://www.siliconmicrodisplay.com/st1080.html
A useful wearable augmented reality experience would require a retinal scanning display, which is presumably what Google's prototypes use. Brother has been showing off a product like this, but it has been nothing more than expo fodder for the last few years: http://www.brother.com/en/news/2010/airscouter/
Retinal scanning display. Hm… I wonder how good this really looks? I didn't find a review video by a independent party. So I remain doubtful as long as I don't experience it myself.
A useful wearable augmented reality experience would require a retinal scanning display, which is presumably what Google's prototypes use. Brother has been showing off a product like this, but it has been nothing more than expo fodder for the last few years: http://www.brother.com/en/news/2010/airscouter/