A simple script for mental ray, which will give you a toggle for Global Illumination that you can have in a toolbar, quad or floater.
I created this as I found myself often turning GI on and off to test various assets in a scene in isolation.
-Extract the ui folder to your root directory of your 3ds max install. (e.g C:\Program Files\Autodesk\3ds Max 2009)
-Put the GI toggle.ms script anywhere you want - as after you have run it, you can delete it.
-Run 3ds max, go to Maxscript>Run script and pick the GI toggle.ms.
-Now go to Customize>customise user interface>toolbars>category GI Toggle - and drag the action to one of your toolbars. Same can be done to put it into a quad.