How do you feel about a ball cap and a sun buff? I have a boonie hat, but even that is a bit cumbersome for my liking. I kind of remember that Outdoor Research makes some nice full brim sun hats.
This one caught my attention being waterproof and UV rated:
http://www.outdoorresearch.com/en/ca...view/id/56718/
These are super popular in my hometown and probably your most effective choice:
