His apparently unhappy life was written about in the recent autobiography of his troubled, but still living, "Diff'rent Strokes" co-star, Todd Bridges, which was the subject of an unexpectedly interesting essay/review by Victorino Matus in the Weekly Standard.
It's currently behind the Standard's pay wall. But maybe in light of Coleman's death they'll make it public (UPDATE: it's now public). In the meantime, Matus adds this on his blog.
Rest in peace, li'l buddy. If anyone feels moved to post favorite Coleman links in comments, please go for it. If I come across the footage of Coleman as pint-sized security guard, one of my favorites, I'll update it.