OK, as a new member I thought I might as well post a new tutorial. This one explains how to make a nice lightning background for perhaps a sig or other projects.
1. Create a new document, RGB with a transparent background. The size doesn't matter, really. I'm making mine 400x100.
2. Go to filter/render/clouds.
3. Go to filter/render/difference clouds. Hit CTRL+F until you get an image with narrow black lines running through it.
4. Invert the picture (image/adjustments/invert or simply CTRL+I).
5. Open the levels option (image/adjustments/levels or CTRL+L) and change the text box in the middle to 0.1.
And there you have your lightning. You could add some color to it with the color balance option if you'd like.