Same here. I only use DM to specifically refer to myself when I'm running D&D. If I'm running another game, I use the appropriate term for the game I'm running (Storyteller, GM, etc.).
When I'm just referring to general game master kinds of stuff, I use the phrase GM.
Other: depends on the game. I'll use generally whatever the conventions are in the particular game we're running: DM for D&D, Storyteller for WW, Keeper for Cthulhu, etc.
My default term when speaking about role-playing games in general is GM, though.
DM when running D&D.
GM for all other games. Even if that game has picked out it's own goofy little name for GM. I GM Spycraft (which has a GC), Traveller (which has a referee), or Storyteller (which has a... Storyteller.)
DM and GM are pretty interchangeable and thus I alternate randonly beetween them. When saying the full words, I prefer to go with dungeaon master because the way I say it 'game master' sounds just like 'gay master'.