I do many of the things already mentioned. I found that a sweat cap under my helmet actually keeps my head cooler and drier; I don't have much hair, but seem to have plenty of sweat glands! Slowing down the last couple miles, so my body has a chance to cool down with the bicycle-generated breeze helps a little.

I am still learning about what works for me for riding clothes, but wearing the lightest clothing possible for the day's weather helps.

There are some that swear by merino wool tshirts and such, haven't yet taken the plunge but considering it.