On my last photo workshop in Italy the weather was pretty dramatic and as I was driving through the landscape a double rainbow formed. I was lucky to arrive at a resonable spot to make a photo of it.
I used my Canon 16-35 f/2.8 at 16mm to capture the entire double rainbow. The post processing is done in Lightroom 3 and a few colored posts to mark the road were removed in Photoshop CS5 with the new content aware fill function. I also used the graduted filter in LR3 to darken the sky slightly above the rainbow.
Regards,
Hans Kruse