Zymic

Create a new 400x100 document with a transparent background (400x100 is my preferred size but anything around there will do.

Press D then X to reset the colours to black and white.

Go Filter > Render > Clouds.
Your image should now have a black and white cloud like effect. Make sure you get a good balance of black and white and make sure it all looks blended.
If not, press Ctrl+F to repeat the filter.

Go Filter>Sketch>Chrome. Enter in these settings:
Detail: 10
Smoothness: 0
(NOTE: Adjust these settings to what you think looks like the best plasma effect.)

Your image will now look somewhat like this:

Duplicate the layer by right clicking on the layer and selecting “Duplicate Layer” Press enter when the confirmation screen comes up.

Click on the duplicated layer and go Filter > Texture > Patchwork and enter these settings:
Square Size: 1
Relief: 1

Press Ctrl+U to colour the layer. Click on colorize down in the right hand corner and enter these settings:
Hue: 125
Saturation: 25
Lightness: 0
(Don’t worry if it looks green for the moment, its meant to!)

Then click on the arrow above the layer (Blending Options) and set the option to overlay.

And finally, click on the background layer and colorize it. Click on colorize again down in the right hand corner, but enter in these settings this time:
Hue: 241
Saturation: 40
Lightness: +15 (This must be adjusted manually for the best effect.)

And there you have it! An awesome plasmatic tiled effect! This tutorial is extremely customizable and you couild have stopped numerous times through out the tutorial and still got a great effect, so go and add some of your own effect (e.g text, borders, etc.) and you will end up with something like this: