Posted around online in the past few days is a PDF copy of Valve's handbook for new employees. It walks through everything from company structure, to gauging your own performance and what is expected of you. Seeing how such a successful company operates is fascinating. From how employees organize projects to just the overall tone of the document. It's a long read but damn, I recommend reading it cover to cover.
I've re-uploaded it here incase the original link I found becomes unavailable and also for a more permanent record for my own memory.