I'm currently reading the Saki short stories again, which I think are not especially well known. They are bitingly funny, incisive and cutting, but can also be incredibly bleak.
I just finished reading one of the longer ones about a mother who becomes estranged from her feckless adult son and I HOWLED - it's just too real. I have an overwhelming urge to go wake my boys with hugs (I won't. They would not thank me. But still). I strongly encourage anyone with mildly exasperating children to read just that story, if none of the others, purely for perspective.
Please recommend your own less-well-known gems 