Ask Slashdot:Programming Styles

David Eisner sent in this Ask Slashdot. It's quite different then usual, but I think it's a really interesting one. He asks "To become a good writer, one studies the works of great writers. To become a good programmer, perhaps it would help to study the works of great programmers. It has always surprised me that this isn't part of the formal training of a programmer. My question, then, is this: What do Slashdot readers consider to be the great works of programming literature? Programs that made you think, "Wow! This is beautifully designed!", programs worthy of study."