Inexpensive but decent sunglasses?

[OakLeaf]

Good point.

Polycarbonate lenses naturally block UV. Polarized glass lenses need to have a UV-blocking coating (and obviously glass lenses aren't the safest choice for sports). Polarized polycarbonate lenses tend to be expensive.

ETA:

From Eye Care Professional magazine:

Although the benefits of polarization are excellent for almost all patients and outdoor activities, some visual activities may be hampered by polarization. Pilots who operate aircraft with polycarbonate or tempered-glass windshields may be distracted by the stressed, checkerboard pattern that may appear in the material. Activities that may require use of a LCD screen may also be hampered by polarized lenses since LCD screens operate by polarizing light. An additional activity that may pose a danger to individuals wearing polarized lenses is downhill skiing. Glare for high speed skiers is a safety asset due to its ability to alert skiers to ice patches and bumps on a ski slope.

So in addition to the nausea-inducing properties I referenced, they could keep you from seeing your computer. I would think that the ability to see reflected glare from ice and water puddles would be an issue on the bici, too.