Coppertone Sport SPF 50 (in the blue bottle) seems to be the best I've found. It's used almost exclusively in the sailboat racing communities, particularly in sunny areas like south texas.
It might be greasy for the first 5 minutes while it dries/cures but after that you don't know it's there. We usually reapply every 3-4 hours as we're in direct sun for 5-8 hours typically