I never use the command reference because, hey, what are man pages for, but I constantly refer to the shell, awk and make chapters, and often dip into the rest in the thick of battle. The one book I take everywhere (except the toilet).
'Cos you need to program Perl. An excellent read, and a complete reference - wish I had time to finish it. Almost worth it for the footnotes and examples alone.
Will teach you more in a shorter time than the above, providing what you need to do falls within the scope of one of its "recipes", which it probably will.
More than just a HTML reference, less than a tedious "Web in 21 Days" tome, this covers all the essentials and gives sensible style tips. It makes some gentle recommendations on following standards whilst remaining non-judgmental, so you can continue to use attributes and TABLEs in ways unapproved by the HTML purists. However, when discussing tools, it only covers Mac and Windows software - so, for example, Photoshop is covered while the GIMP isn't.
LaTeX is the only choice if you want to write large documents with the benefit of hundreds of years of typesetting knowledge. Unfortunately, it can be a pig to drive unless you have these books. Then suddenly, you realise that you can do whatever you need in LaTeX. And life becomes a whole lot better again.