Biking around, I find that the visors on the helmets really do a poor job keeping the sun out of the corner of your eyes.
So, just take a normal sheet of 8x11 paper, round the edges with scissors, and then tape it to the top of the helmet.
It gets curved by the shape of the helmet to get stiff
enough to not bend in the breeze.
1. It gives custom coverage (just snip less / tape more).
2. Collapses easily in case of crashes (unlike other visors which can push your helmet back and expose your forehead).
3. Easily replaceable in case it gets wet or damaged.
4. Free (use scrap paper)
For the delux version, use scrap paper of a higher quality (thicker, or partially laminated, etc).
If you're afraid this makes you look goofy, well, you are already wearing a bike helmet, cool dude.
Your comfort and eyesight are worth it.
FYI: I've been doing this for a few years, but seem to be the only one around here...