TeX

Achim Blumensath: Download
Contains manual and source code for Ant which is a typesetting system similar to TeX written in Objective Caml. Various LaTeX packages are also available.
http://www.mathematik.tu-darmstadt.de/~blumensath/Download.html

AMS TeX Resources
TeX-related style file collections, fonts, manuals, and author packages for preparing submissions to American Mathematical Society publications. Platforms: PC (DOS and Windows), Macintosh (for Textures, OzTeX or CMacTeX), and Unix.
http://www.ams.org/tex/

CTAN
The TeX Archive Network is a set of fully-mirrored ftp sites providing the most complete, up-to-date TeX-related software possible.
http://www.ctan.org/

CTAN Search
Online search interface for CTAN. Search CTAN for a file or search the TeX catalogue by Graham Williams for a keyword.
http://www.ctan.org/search/

Donald Knuth's Reward Check
An example of a reward check by DEK and how to get one.
http://truetex.com/knuthchk.htm

Interesting TeX-related URLs
Maintained by TUG.
http://www.tug.org/interest.html

Knuth: Message about TeX Fonts
Important message to all users of TeX.
http://www-cs-faculty.stanford.edu/~knuth/cm.html

(La)TeX Navigator
A (La)TeX encyclopaedia from Loria. Also available in French and German.
http://tex.loria.fr/english/

Mathematics For Computer Generated Spoken Documents
AsTeR --Audio System For Technical Readings-- is a computing system for rendering technical documents written in LaTeX in audio.
http://www.cs.cornell.edu/info/people/raman/aster/demo.html

TeX Merchandising
Merchandising for TeX and friends. On-line ordering with PayPal.
http://www.dream.kn-bremen.de/tex/merchandising/

TeX Resources
A list maintained at U Penn.
http://www.math.upenn.edu/TeX.html

TeX showcase
Examples of professional TeX typesetting of books in the humanities, selected by the Association of American University Presses.
http://www.tsengbooks.com/

The TeX showcase
Edited by Gerben Wierda, it contains examples of what you can do with TeX, from typesetting of scientific papers to music, multimedia, genealogical presentations, dynamic documents, multilingual documents.
http://www.tug.org/texshowcase/

The TeXability Site
Shows short (mostly single page) documents with immediate access to graphical results and source to demonstrate the power of TeX.
http://texability.corlan.net/

TeXblog - Typography with TeX and LaTeX
Collects useful information about TeX and LaTeX and lists solutions found for often occurring or interesting problems. Further it provides an archive of links regarding TeX and LaTeX.
http://texblog.net/