For even those who are very new to 3D
art in general, whether it be viewing
or making, it is very likely that you
have run into a render that looked very
much like it was made of clay.
Example:
I will be teaching you how to render something in this "style", which i stress, is to be only used to show a model that has yet to be textured, since, if this technique is used with textures, they will be washed out.
Open any object you want, but adjust the colors of the individual surfaces so that they are, at most (brightest), 150,150,150. The next part is the reason as to why your textures will be washed out when using this technique.
Change the cumulative intensity of the lights in your scene to about 25% (with only 1 light, adjust to 25%, with 5, to 5%). Most definition of the object will then be lost.
Now open the GI (global illumination) settings (under LIGHTS tab), and make sure GI intensity is at 100%. Enable radiosity at 100%, and select Monte Carlo as its type. Enable 'Shading Noise Reduction' as well.
Select the SCENE tab, and change the backdrop color from whatever it is currently to white (255,255,255). Enable antialising and set its level to medium. This will assist in reducing the noise left by the radiosity.
If all the steps were followed accordingly, when you render, the resulting image will bear that Clay look.
More 3D Graphics: 
