2k1Toaster, windscreen film: I haven't considered putting some sort of film on the screen, but it sounds like an idea. Will consider it. Might be illegal here, though.
Bugbyte: how-to: It seems like many of you are interested in this project, so sure, I can write a guide.
MeeM, piglith: I am not sure if a standard LCD/VFD display would be bright enough in broad daylight, but on a cloudy day or at night, both would be usable. Maybe a standard TFT monitor with brightness on full could be used for a large HUD? Do go ahead and test it!
Colin: The very cheapest way to do this would probably be to get two USB-to-parallel converters, add some led drivers and then connect the displays. However, it would be somewhat bulky and require quite a bit of soldering and fiddling, and remind me too much of http://www.afrotechmods.com/ , so I chose a Fusion Brain. I do agree that it is slightly overkill, though.