I don't know about other developers, but I have a lot of trouble working if I don't like my surroundings. I need to have at least somewhat clear desk, lots of light, and preferably a window. Blank walls depress me, and I tend to cover them with colourful posters and hangings. But aside from all that, I haven't paid much attention to what specifically decorating the area around me when I work.
In my reading of game dev articles around the internet, I came across a recommendation that even programmers keep concept art for the game they are working on up around their work space. The idea is that good concept art can not only keep devs inspired, it can help maintain the overall aim and feel of the project. Because of this, I've decided to cover the bulletin board above my desk with concept art for the projects I'm currently working on.
Having not worked with professional artists before this year, it's really awesome to look up and see a bunch of concept art all based around something I'm working on. Hopefully this idea helps keep others out there inspired! If anyone else opts to try this out, feel free to post pics of your work space in the comments!