I'm surprised nobody else bothered mentioning this: Hands, feet and ears. For an hour-long ride, keeping your legs/arms/torso warm is not particularly hard, but extremities are, because you're making your own 20-30mph wind. I recommend expedition-quality gloves, a balaclava, and something along the lines of sock liners/covers (might need to check shoes/helmet for fit with all that underneath). Not a particularly big expense though.