TeX by Topic [eijkhout.net]
TeX reference manual
Links to additional TeX, LaTeX, ConTeXt and CTAN info.
This document explains how to use imported graphics in LaTeX2e(pdf).
A list of all the symbols and characters that can be produced with LaTeX-in pdf format.
A nice site with relevant links to LaTeX. It has beginner,amateur, and professional pages with corresponding links appropriate to each level. The links in the professional section point to additional LaTeX resources which provide a starting point to discover more documentation than you could possibly ever want to read. The site also has links to other useful info like Vim.
The TeX Users Group (TUG) was founded in 1980 for educational and scientific purposes, to provide an organization for those who have an interest in typography and font design, and are users of the TeX typesetting system invented by Donald Knuth.
Information about the American Mathematical Society’s AMS-LaTeX package for typesetting mathematical formulas and expressions.