My service issue Mags for vehicle carry and supply the normal Maglite plastic brackets which come in a set of two. To my mind whilst these are adequate they are not aesthetically pleasing or particularly strong.
At home and on a duty belt I've used a Lite-Lok which was made by Safariland but is now sold under the Nite-ize banner. These things are great as they take loads of punishment and keep the light secure. They have the advantage of looking good and can be mounted on a wall or belt easily.
Personally I wouldn't ever consider carrying a 4D Maglite on a belt. Come to that I don't think I'd ever belt carry a D size Maglite anymore as they are too large and cumbersome. However I have the C size Lite-Lok and a modded 2 C cell Maglite which I would belt carry if I didn't have access to something better.
If you check out the Nite-ize web site I'm sure you can see the Lite-Loks on there.
Doug