A molded plastic sun visor replacement that 'accordions' (concertina - like some straws and sippy cups do) down to block glare.
I'm thinking of slightly tinted transparent plastic so you could actually see through it in the areas where it's fully expanded.* If you want more tinting - even in the
middle of the visor - you could adjust** the folds to partially collapse, increasing the tinting.
Because it's transparent, it could be made so it expands to a decent size - say 1.5', though fully extended it won't block much light. It should collapse to about 3" or 4" so it's never in the way. It should also remain on a swivel (like a normal sun visor) so it can swing to cover the side window as well.
Some folks will complain about the missing vanity mirror. I say shouldn't you be watching the road?
*Not recommended for driving purposes
** Please adjust visor while vehicle is not in motion.
(March 10,2002: modified to sprinkle the word 'concertina' throughout as it better expresses the intent of the idea)