This is an effect i discovered incidentally while clicking here and there. It is not exactly very cool, but i think it is quite useful as some kind of a background. Of course, it is a very basic technique, but just take a look:
http://i3.photobucket.com/albums/y76/sceptileex/rot.gif
First, start a new page, white background, 500x500
Then, use Filter>pixelate>mezzotint
http://i3.photobucket.com/albums/y76.../mezzotint.gif
Then, use filter>blur>radial blur, with all default settings, using zoom
http://i3.photobucket.com/albums/y76...alblurcopy.gif
The next step is to do Filter>Distort>twirl. Set it to about 30 to 60, depending on your preference.
http://i3.photobucket.com/albums/y76...leex/twirl.gif
Then, use hue/saturation to colour the twirl to your colour of choice.
http://i3.photobucket.com/albums/y76/sceptileex/rot.gif
duplicate the layer and try out different effects. This is a background you can use for your sigs. Enjoy!
(sorri for the bad images, i lost the images on my com... too lazy to make a new one... sorri...)