In July 2010 I took a two week road trip out west. This was one of my favorite photos from the trip. On day one we made it all the way from Milwaukee to the Badlands of South Dakota.
Just as we arrived the dark storm clouds dumped a bunch of rain. Initially disappointed, it turned out to be a blessing in disguise. The rain brought out a ton of color in the soil and as we were driving out of the Badlands we just happened to see this double rainbow forming.
Oddly enough, this was taken with my new iPhone 4, and it just shows how great that camera can be.
Update: As seen on Mashable, 15 Fantastic iPhone Photos of Rainbows. - September 5th, 2011.