6 links
Knuth: Computers and Typesetting
-cs-faculty.stanford.edu
Don Knuth's page for the TeXbook, METAFONT book and the Computers and Typesetting set. Errata and procedures for reporting bugs and mistakes.
Making TeX Work
makingtexwork.sourceforge.net
A book about using TeX and the complete TeX environment. Written by Norman Walsh and (re)published under the GNU Free Documentation License.
The PracTeX Journal
tug.org
Dedicated to the exchange of practical experience and instruction of the use of TeX and other TeX-related or TeX-derived systems.
Wikibooks: TeX
en.wikibooks.org
A collaboratively written guide to the basic engine for macro languages (formats) as Plain TeX, LaTeX and Context.