I have been looking for one since I got my touch screen pc with no VGA port, I need a USB to VGA with HD 720p video support so I could watch HD videos (from local files, not BLU-RAYs). I looked at the DisplayLink adapters but I am unsure which ones support HD videos, adapters on Ebay do not mention it either so I suppose they do not support it. Thanks for any ideas, they will be appreciated.
My best suggestion would be checking out newegg.com. I personally would go with the Kworld UD160. It is an excellent price and the adapters it includes to support DVI, VGA, and HDMI are quite handy. It doesn't say so in the specs, but I am pretty sure it supports 720p. It also has the highest resolution support I can find for these.