Rigidbody objects drop and embed into BoxCollider surface

I have a few cubes that are Rigidbody objects placed directly on top of a rectangular BoxCollider surface. Every time I test the scene the cubes drop a little bit into the surface beneath them? Any way to correct this?

Thanks,

Greg

In the Physics Manager decrease the Min Penetration For Penalty variable. This says how far an object sinks into another.

Here is a link to the documantation:

http://unity3d.com/Documentation/ScriptReference/Physics-minPenetrationForPenalty.html

Thank you Daniel, I appreciate your help very much!

-Greg

also there's a cool script on the wiki if you need to "presettle" your physics objects:

http://www.unifycommunity.com/wiki/index.php?title=TransformSaver