Innovative as it may be, the Steam Controller is not flawless. Everyone has their own complaints about it, but if your complaints are related to the shape and size of the thing, now's your chance to take matters into your own hands. In this Steam Community announcement, Valve released CAD data for the controller in various file formats so that folks can use their tool of choice to fiddle with the files.
The package includes all of the geometry from the controller itself, as well as a few example backplates that are designed to hold the controller's USB wireless receiver. The data is being released under Creative Commons, so it's freely redistributable—as are any models the community creates. Tinkerers will need to contact Valve if they wish to sell their creations for money, however.