Canon 580EX II
I use the sun as a backlight quite a bit. A bright sunny day can be the worst kind of day to take portraits. For 35 years of my photographic life I have been told to take photos with the sun to my back. I will only do this if I have no choice or if the sun is diffused by clouds.
I have a new giant softbox that we were trying out. Using only the pop up flash from the Canon 7D as a master, I held a Canon 580EX II flash in the softbox and took some portraits. The flash head on the 580EX II can be turned completely around so the IR sensor is pointing toward the photographer.
Click on any photo for larger view!
I encourage you to try fill flash on the next sunny day using the sun as a back light. Be sure and get the flash off the camera in the true strobist way.