I like the kind of wallpapers where fire or colors are shown like they'd flow as water does. Browsing through a large image-stock-site I found some which were completely free for all usage.
I put together the two best of them and worked with scanline-effects and wind-effects - creating smoothness & roughness, all visible through scanlines.
I made three versions of the image in different colour-sets: B&W / W&B and black / fire.
Images made using: -The Gimp