I learned about the general premise of making my own dual-screen wallpapers from videojug. Below are some wallpapers I use on a regular basis. I use Photoshop or GIMP and the source file is set to 300dpi. That way I can resize images without losing quality. The final product is reduced to 72dpi. You can leave it at 300dpi if you want. I did that so I can share the files easier.
Dual-Screen Gallery
Niko Bellic from Grand Theft Auto IV. [1256x1024 pixels]
The two opposing forces in the world of Transformers. [2560x1024 pixels]
Concept art from Mass Effect 2 [2560x1024 pixels]
Saren Arterius, a former turian Spectre, from Mass Effect [2560x1024 pixels]
The infamous duo, Ken and Ryu from Super Street Fighter IV. [2560x1024 pixels]
Some of the characters in the Street Fighter universe. [2560x1024 pixels]
A look at the core fighters of Super Street Fighter IV. [2560x1024 pixels]