Comics artist Alex Garner whipped this Portal 2 tribute up in his spare time. It feels strange calling it fan art. There should be a better name than that for pieces like this.
As the original image wasn't in wallpaper dimensions, and it's so damn pretty people are going to ask, I've taken the liberty of putting together a 1920x1080 version, which you can grab here.
Portal 2 [Alex Garner]