Access the on-line FAQ compiled by the UK TeX Users Group for answers to Frequently Asked Questions on TeX-related topics.
To obtain a printable version, go to CTAN and select a file named "letterfaq" for your own reference use.
This file is formatted for U.S. letter-size paper. An A4 version is called "newfaq".
The file is available as a TeX source, as well as in .dvi, .ps and .pdf form. If you retrieve the TeX source, you may also need some style files, in the same directory.

LaTeX Topics

Catalogue of (La)TeX macros and styles
The CTAN edition of Graham Williams' LaTeX Catalog Online lists and describes briefly many (La)TeX tools and packages, most of them available on CTAN.
A LaTeX bug?
Before asking for help, check the LaTeXbugs database.
Bug reports include the problem statement and examples that trigger the bug, as well as (possibly) discussion, workarounds, and, for bugs that have been resolved, a statement of what was done and the applicable LaTeX version.
Topics covered (among others): LaTeX, AMS-LaTeX, Babel, Graphics and color, Metafont fonts, PostScript fonts, and Tools.

General TeX discussion lists

Usenet newsgroup: comp.text.tex
Read current messages with a Usenet news reader.
A public news reader on the Internet is found at groups.Google.com.
Electronic TeX Digest: TeXhax
Send messages to TeXhax@tug.org.
To subscribe or view the archives, visit the TUG TeXhax page.

Discussion lists for particular TeX implementations

MikTeX
To subscribe, follow the instructions at the MikTeX website. This page also contains pointers to the list archives.
fpTeX
Send correspondence to fptex@tug.org
To subscribe, add your name to the mailing list at the TUG fptex page.
BaKoMa TeX
Enter a subscription from the web page http://groups.yahoo.com/group/BaKoMa.
EmTeX
Send correspondence to emtex-user@physik.tu-berlin.de
To subscribe, send a message with one line in the body, saying
subscribe emtex your name
mail to: majordomo@physik.tu-berlin.de
4AllTeX
To subscribe, send a message with one line in the body, saying
subscribe 4tex your name
mail to: listserv@nic.surfnet.nl
List archives can be found on the Listserv archive site at SURFnet.
OzTeX
Send correspondence to oztex-info@maths.adelaide.edu.au
There is a separate moderated announcements list.
To subscribe, send a message with one line in the body, saying
subscribe oztex-info
or
subscribe oztex-announce
mail to: majordomo@maths.adelaide.edu.au
Before sending a question to oztex-info, see if the OzTeX FAQ has the answer.
iTeXMac
Lists and archives for news, help, and developers are accessible from a link on the iTeXMac home page.
TeX on Mac OS X
To subscribe, follow the instructions at the MacOS X TeX/LaTeX Web Site using the Mailing Lists link on the left hand side.
That page also contains pointers to digests of the archives.
teTeX
Send correspondence to tetex@dbs.uni-hannover.de
There is a separate moderated announcements list.
To subscribe, send a message with one line in the body, saying
subscribe tetex
or
subscribe tetex-announce
mail to: majordomo@dbs.uni-hannover.de
Pointers to list archives are on the teTeX web page.
LyX
There are lists for announcements, users, developers, documentation team, and more. All are archived.
For details, see the LyX mailing list web page.