I just bought a Respro Foggy Anti-Fog Breath Guard from mspeed http://www.mspeedperformance.com for aboot $35 and give it two thumbs up, way up! Well worth it.
This thing rocks! I've been riding for days now without any fogging of my visor. I haven't hand to crack open my visor yet, which I was always doing on cold mornings or when raining.
Check it out here: http://www.respro.com/popup_foggy.php
Not affiliated with mspeed or Respro. Just thought I'd share.