Some Online TeX and LaTeX Resources

TUG's Getting Started with TeX, LaTeX, and Friends.
Links to lots of resources for getting started learning and using Tex, LaTeX, and, well, Friends!
TUG's TeX and LaTeX Documentation.
Formatting Information: A Beginner's Guide to LaTeX, by Peter Flynn, Silmaril Associates
A good, detailed, introductory guide covering the use of TeX and LaTeX on Macs, Windows, and Unix/Linux systems. Available in HTML and PDF.
CTAN—the Comprehensive TeX Archive Network
CTAN maintains a comprehensive archive of TeX and LaTeX packages, formats, fonts, document classes, documentation, and other materials, including complete TeX systems.
We maintain our own local CTAN mirror, as well.
The UK-TUG FAQ
Answers many frequently asked questions about TeX and LaTeX. A good first place to check if you're having problems.
Detexify LaTeX Handwritten Symbol Recognition
Cool site that lets you sketch a symbol using your mouse, then suggests LaTeX symbols that are close to what you've drawn. Often a good way to figure out what command to use for a particular symbol.
Comprehensive LaTeX Symbol List
A document showing a huge array of symbols, the commands that produce them, and information about the packages that provide those commands. (Available on many TeX systems as symbols-a4.pdf or symbols-letter.pdf. Try running texdoc symbols for a viewable version or texdoc symbols-letter for a printable version.)
LaTeX Search
Allows you to search for equations in Springer journals and gives you the LaTeX code to create those equations. Should be useful both for referencing work in Springer journals and for getting sample code for equations that are similar to what you're trying to write.
comp.text.tex
comp.text.tex is the official Usenet newsgroup for discussing TeX and LaTeX questions. Chances are that any problems you're having, someone else has already had, asked about on ctt, and gotten an answer. You can search the newsgroup with Google.
Google
Google is probably your best bet for finding information outside comp.text.tex, as well.
TUG, the TeX Users Group
TUG is the main international TeX User Group. TUG runs annual conferences, maintains and distributes the TeX Live CD-ROM, and supports the work of the LaTeX Project Team.
The PracTeX Journal
The PracTeX Journal is an online journal on TeX and LaTeX issues that welcomes contributions from readers. A typical issue will have articles ranging from answering basic questions to in-depth discussions about how some complex problem was solved.
Using Imported Graphics in LaTeX and pdfLaTeX (PDF)
Keith Reckdahl explains how to include graphics using the standard TeX->DVI->PostScript and the newer PDFTeX->PDF approaches to TeX compilation. He also talks about the different graphics formats available and their advantages and disadvantages, explains how to include multiple images in a single figure, and comments on some of the software applications available for generating and manipulating images.
Donald E. Knuth's Home Page
Knuth is the author of TeX, and a renowned computer scientist. He's mostly offline, but does maintain a webpage with some information about his work, past, present, and future.
My take on TeX and LaTeX books