So, awhile ago, I was using RenderMonkey, a GLSL shader tool, and it shipped with a pre-made electricity shader. I have since readapted it to work with the BGE. :D
You can find a video of it below.
Requires Blender 2.5+ to work. Here's the download.
EDIT: Aaaand I forgot that the shader relies on a noise texture and didn't pack it in. -_-
I fixed the downloads.
Mirror 1 - PasteAll
Mirror 2 - MediaFire