If I had no responsibilities to myself or others, I'd do all of my summer running early in the morning, during the coolest part of the day. Since sleeping at my desk is not an option, though, it's better that I get that extra hour or two of sleep before going into work. Running, therefore, is relegated to immediately after work, during the hot part of the day.
One of my heat-beating schemes is shown above. It works great for the first 10 minutes or so, which is a lot better than not at all.