left to right - null object, null object selected, null object with
widget prototype installed
The Null object is an ordinary mesh with a camera and a null object
encapsulated within. The camera fools the renderer into thinking
the null is a camera so it doesn't get rendered.
Download the Null object
here
When selected the null object will display with a camera over it.
The Null Widgets script will tell truespace to reinterpret the null as a
null object instead of a camera and the normal object navigation widget
will display in the center of the object.
Download the Null Widget script here

click the picture
Any mesh can be converted to a null by running the Convert2Null script.
This script adds a camera and a null to the mesh.
Download the Convert2Null script here

click the picture
The Null will be invisible in lightworks, modelspace workspace renders
and probably in v-ray as well. The Null objects and lights are
visible in the realtime renderer. The Null and Lights Visibility
script allows for setting the visibility of all Nulls, Lights or both.
Download the Null and Light Visibility script here

click the picture