Hi! I had luck when i pointed my camera at some dark clouds. Some impressive flashes happened. I have slowed the video down from 25p /sec to 1p/sec.

It is encoded as ogg theora, because that is the only format allowed on wikipedia commons.

http://commons.wikimedia.org/wiki/Image:Flash-Lightning_over_Germany_slowmotion.ogg

You can use it for whatever you want. I release it into the public domain.

greets
Stefan