I fold a bandana in half and tie it around my head so that the knot sits lower than the back of my helmet and the front is even with my helmet. I find that this deflects the wind from my ears quite effectively, but does not cause me to overheat.

When it gets colder I wear a fleece headband, but it's too warm for that this time of year so I stick with just the bandana until the temps drop below 15ish.

For my face, I wear a beard which is surprisingly effective at keeping me warm.