I would agree with Steve on this, for showing off details on a model then doing an ambient occlusion render in Mental Ray is ideal.

On the otherhand to show a fully rendered model with colour I would try:

HDRI Map
1x Directional Light (Main Light)
3x Ambient Lights (Fill Lights)

Then start to adjust the intensities, I would suggest 0.5 for the main and 0.2 for the fills. As I have recommended the use of a HDRI Image, and also render with MR and FG.