It's been a while since I've gimped a wallpaper, but here's something I just knocked up.. the GitHub guys have an .svg of their logo in the stylesheet, so I assume they don't mind people using it ;)

A 1900 x 1200 high-res version is hosted on CloudApp

~~A high-res version is hosted on flickr.~~

UPDATE: The largest resolution on flickr is 1024 x 640 so I have added a link to the largest version I have.