I'd start with the best collection of his short fiction that I've read, simply titled The Best of Cordwainer Smith, edited by J. J. Pierce, who is a Smith scholar. My copy is a Baen Book, and I don't know if it's in print, but you can look. Smith's real name was Paul Myron Anthony Linebarger (1913-1966.) He was a godson of Sun Yat Sen, a diplomat, a spy, a CIA specialist in brainwashing, a man who loved cats, and is as fascinating a character as any he wrote about. He only wrote one novel, "Norstrilia," but it is part of his imagined universe, with loads of characters who show up in his other stories.
My personal favorites are the novel, followed by "The Ballad of Lost C'mell" "The Dead Lady of Clown Town," "The Game of Rat and Dragon," "Under Old Earth," "Alpha Ralpha Boulevard," - wait, I'm naming too many. But they are all magnificent, and strange. When it comes to stuff on the web, you can try this excellent wikipedia article and his daughter's web page on him.

Hope I haven't given you TMI, but his stuff is so marvelous, I'll risk being labeled a tad obsessive in order to introduce other folks to him.