I prefer wearing long sleeves for protection from the sun. I've been using Hanes "Cool Dri" tee shirts, and low cost Nashbar jerseys, some of which are pretty thin. Both work fairly well, and are economical, but I wouldn't mind spending more if there is something that would be even cooler.

I bought a pair of Desoto "arm coolers" several years ago to wear with short sleeves, but never really took to them... they didn't feel cooler than the setups mentioned above. A garment that is a little "loose" and not skin tight seems better to me since it offers airflow.

Is there a cooler long sleeve option for hot weather riding in the sun?