This is a Google Video of a 500kV switch opening in the Nevada desert. I really wish I could have been there.

Also check out a 345kV switch opening. This story got buried on digg. I’m not sure how something so popular got buried, but I saved something from the comments:

As the switch first swings open, the gap is very small and the voltage makes an arc as it breaks down the air (turning it from an insulator to a conductor.) Once this arc is established it grows in length as the switch is opened further since most of the air between the switch contacts has already been rendered conductive. Notice that the arc rises as time goes by because the arc heats the air and hot air goes up. The arc goes through the longer path because that hot air that is rising is still more conductive than the cold air down below which replaces it. Eventually the conductive air rises enough that the path through it has to also go through the colder non conductive air and this breaks the arc.