I spend a lot of time in the sun. In fact, I just came home from 10 days in Yuma, AZ and Mexicali, MX where it was 125 degrees.
I always wear sunscreen when I know that I am going to be out in the sun for more than than 15- 20 minutes straight. I hate greasy anything, so I use Neutrogena sheer mist spray. I love that stuff. Goes on dry and stays on even when swimming.
When I am out on the bike I wear a biker bandana/skull cap.
When I am walking around in super hot temps I wear a Panama hat with a wide brim to prevent sunstroke. (your brain really can cook in the the 100+ degree temps you know!)