So far, this has been a great week for finding useful Unix/Linux reference on the Internet. The Unix Toolbox is a very lengthy, yet concise reference.
> This document is a collection of Unix/Linux/BSD commands and tasks which are useful for IT work or for advanced users. This is a practical guide with concise explanations, however the reader is supposed to know what s/he is doing.
Colin Barschel is the author of the reference guide (and has made it available as a PDF as well). The main site is a lot of fun as well. It’s a terminal.