There’s an entry at Lambda the Ultimate pointing to notes from a talk given by Stephen Wolfram. I’m just skimming through it myself, so I’m not sure where it eventually ends up :-) But even just some of the information on the first page is worth mention. Almost immediately he starts explaining cellular automaton, and certain automaton that display behavior which seem to display random behavior. The explanations have been amazingly simple and accessible. Peppered throughout the talk are references to A New Kind of Science, a book with what looks like the full text available online.