Blender: open source graphics software
Last, but very certainly not least, is Blender—an open source, cross-platform suite for 3D creation.
Blender is capable of stunning 3D work—and not just still images. Blender has been used to create animated masterpieces like Big Buck Bunny and Elephants Dream. (See a list of movies from the Blender Foundation on the Blender site.)
Few small businesses will need this kind of power, but Blender is on par with proprietary tools if you have need for 3D modeling and such. If you're running a small art shop, Blender should be part of your toolkit.
Blender is available for Windows, Linux, Mac OS X and more. On the download page you'll also find "regression files" that are meant to test releases of Blender to ensure that updates don't break features artists have come to expect. But you can also use the files to get up to see how things are done with Blender. The application also has lots of docs to get you up to speed.