Vortexes make a really simple looking yet effective background to any graphics. And, they're really simple to make!
First, open up a new page of the size you desire - the background colour is irrelevant at this stage. Next, go to Filters > Render > Clouds > Solid Noise. This will create a grayscale pattern with a vague resemblance to clouds.
Now, to give it that vortexy look, we need to add a motion blur. To do this, go to Filters > Blur > Motion Blur.
This is the important bit now: set the Blur Type as "Zoom" and the Blur Center as the center of your image - you can experiment with different effects using other centers at a later date; change the length to something you think looks good. I'm using 168 though it should ideally be larger than the distance from the edge to your center.
Now, in black and white it still looks boring. Pick a foreground colour and create a new layer, changing the mode to Multiply (you can of course experiment with different modes if it doesn't look good). Use the Bucket Fill to colour your image in.
And there we are, done! I told you it was simple.
Now, you can feel free to experiment with different centres, modes, gradients and backgrounds. Make sure to show us what you achieve though too by submitting work to our Art Gallery