A helmet cover? Yup a helmet cover. It has been raining a bit and before that cold and dark. So I picked up a bright yellow helmet cover from Jandd.
I used it on a long ride in the rain this weekend and it kept all of the rain out and the reflective patch in the front and back made me more visible. I have also been using it while commuting early morning lately too.
Plus the reflective strap on the back is actually a loop so you can attach your blinky light.
Now it is waterproof, so it’ll keep your noggin dry from rain, but it doesn’t breath all that well, but I say the trade off is worth it. As a side, it keeps your head warmer during cold winter commutes.
Its cheap ($15) and made in the USA: http://www.jandd.com/detail.asp?PRODUCT_ID=FHCW