Austrian ski instructors in Arlberg region have agreed to bare it all after students ask them to release a naked calendar. A company spokesman said, "We often get men staring at the female instructors and many women seem to sign up just to flirt with their teachers, so we thought, why not give them what they want?"Apparently this has been a phenomenally successful item for them. I'm not seeing any mention of a charity, though, so this may be a tad outside my target area.
See also Ananova, Kink (1, 2), Natives.co.uk, and the official site at Skilehrerinnen.at (or here). And I believe this page from the Burg Hotel refers to the same calendar. Fair warning: They don't hide behind things.