Recommended from another thread, I just got one of these:
http://www.drillspot.com/products/528027/nite_ize_lhs-03_nylon_holster
Designed to stretch and accomodate up to a D-cell body. Firmly clips on belt up to 2.5 inches and has a rotating function while clipped to belt (can direct light forward while still on belt)
Mine is still very tight but once it breaks in a bit will work very well.
Can't beat the price!
The Nite-Ize holser is what I use for my larger lights, including the M1X. It has a plastic belt clip, and rotates so you can use your light hands free, which is actually a pretty cool and usable feature. The price is right, and as far as I can tell, the quality is great (I have used mine on duty every night for months). This holster works great with 123 and C sized bodies, I wouldn't use it for anything slimmer or thicker, but it does work.
Awesome buy for the money, get 2.