http://www.motorcyclegear.com/browse/se ... ry=pinlock
http://www.webbikeworld.com/anti-fog-visor/
Looks like these are still catching on; not sure if you can find them for helmets other than Shoei, Arai, and HJC. Basically works like double-glazing on windows. The insert has a thin offset bead around its perimeter that creates an equally thin layer of air against the actual shield, but allows no moisture transfer to it.
I got an amber one for my Shoei and I give it 12 out of 5 stars. Installation was easy and it just works. NO fog, full stop.
Even after it started warming up this spring I'd still get fogging at a stoplight and have to crack the visor a notch or two, despite the Shoei's lever setting that cracks the seal a tiny bit to combat fogging. The venting on the RF-1100 is pretty awesome in motion, and other riders have commented they thought it was the coolest (feeling!) helmet they've owned, but it definitely fogs fairly easily (clears right up once you hit 15-20mph assuming a vent or two is open, but still).
No more! If they make these for your helmet and you're tired of cracking your visor all the time, give 'em a look. You can have a single pinlock-ready shield and just carry different inserts if you want. In addition to the improved contrast, the amber reduces enough glare/light that I don't need to squeeze sunglasses inside. Bonus: colors really pop! The world looks kinda bland if you've been riding for a while and take off the lid.
Pic of mine:
YMMV.