I must have told ten people to read Eliezer Yudkowsky’s stuff by now and I keep forgetting to send them links, so this is for all of yez.
Yudkowsky mainly writes on a collaborative blog called Overcoming Bias (motto: “How can we obtain beliefs closer to reality?”). The other articles are ok too, but Yudkowsky is a true visionary and an extremely intelligent guy. I can’t find a list of his complete postings there, but they’re fairly well interlinked so you can just start reading. If you don’t understand something, go on following references to his older posts and you’ll eventually understand what you didn’t before.
He also has a personal site at yudkowsky.net with even older stuff. It has this notice: “Most of my old writing is horrifically obsolete. Essentially you should assume that anything from 2001 or earlier was written by a different person who also happens to be named “Eliezer Yudkowsky”. 2002-2003 is an iffy call.”