I was thinking we should have a thread with photos of all sort of optical phenomena on the sky, such as rainbows, fogbows, halos, arcs, pilars, mirages, glories, sun dogs, coronas etc etc. Being, originally, a meteorologist I'll try to help keeping these different phenomenas appart in case you are not sure what you actually captured.
So I'll start with a shot from yesterday. Primary and secondary rainbows over Stockholm, right after a heavy rainfall, shot from a 100m high tower (in which we make some atmospherically related measurements) with the DA10-17mm fisheye zoom, stitched together from 4 photos in PTGui.
If you have a slow connection you shouldn't click the picture since it will take you too a very large image file.