I wear a Klim Helmet. I love it, it has two liners that snap in and out. One is for winter colder conditions and the other lets more venting for spring. They work well with the 509's also.
One thing I've found that really has cut down on fogging goggles is vented helmets. :cheer2: This is just a side effect, but a good one. I noticed it when I started wearing the Sixsixone Mountain Bike Helmet over the last 2 seasons. 2 things about me, I have neck issues and always seem to overheat. This helmet is where I started noticing a whole lot less fogging with my same old Scott goggles. NICE! But also noticed less neck pain at the end of the day. These things are unearthly light. Some don't trust them as they are not DOT approved, but I look at what downhill mountain bikers do... and I think the helmet will be just fine for what I do.
This year I also got the Fly Formula MX Helmet. I was a bit hesitant due to it being just a tad heavier than the 661. I don't feel it at ALL! This helmet is about as CUSHY as you can get. It feels like there is contact on every part of my head, yet NO pressure points. I still have great venting and have yet to find any limitation of vision. Some MX Helmets, in the past, have limited my range of vision/ peripheral vision. This helmet does not limit me here in any way. :cheer2:
Just wanted to add some info about my Fly helmet. It is supposed to be carbon fibre, but it is still pretty heavy. Rode two fairly long days over the weekend and came out with a stiff neck and crazy bad headache. I feel like my head is floating now with the weight off of it. Can't wait to get my 509!