Aside from the obvious answer that they can turn to the Savior, where are concrete, physical human beings actually within reach to whom Latter-day Saints who suspect they may suffer from mental illness may turn? Some suggestions I have heard from caring individuals on various blogs and in other discussions on this topic are listed below, with a critique of that source from my (limited) perspective. I invite everyone to offer their own perspective so that I, in turn, can offer it to people I know who stand in need of help but are unsure of where to turn.
I appreciate Ronan’s informative post over at BCC– it provides a great starting point. Here are the sources which I see as possibilities to get help, and my comments/questions/concerns regarding each:
Posted by Jordan F. 
ABEV: a bird's eye view 