I use a MagLight belt holder (meant to hold a 2AA incandescent MiniMag). Most MiniMags I see these days come with this nylon holster included in the package. This fits my 1-AA light fantastically ( http://www.dealextreme.com/details.dx/sku.19187 ). It was tight at first, but loosened up with time. The light goes in tail-button down, head up. You can often buy an incandescent MiniMag including this holster for about the same price as buying a similar holster separately. Incandescent MiniMags are around $5 these days if you shop around.

The Deal Extreme light above is fantastic BTW. I've used it constantly (daily) for over a year. Very sturdy and very bright. No flicker either. As long as you keep the threads clean - I'm in the habit of cleaning these every battery change, so I've not had any flicker issues that many others report for many different brands of pocket lights. I use NiMH batteries in it.