"The Ones Who Walk Away from Omelas" is one of my all-time favorites, too...I have so many all-time favorites, but that's way the heck up there on the top of my list.  I've recently discovered a new writer...well...new for me: Aleksandar Hemon.  He writes non-genre fiction, but he's brilliant.  I think I have to now rank him up there with LeGuin.  And his work is extremely inventive (and quite literary in that the manner of its presentation is as important as the story itself).  Hemon is probably a good writer to look at if you're interested in seeing how the short story (or novel) form can be played around with.