Useful sites

A lot of people who provided their dotfile on the web also have provided more general Emacs pages. The notes sections of the dotfile entries on the pages concerning locally available .emacs files and links to the .emacs of other people contain more links to Emacs resources.

GNU-Emacs

the Emacs pages at www.gnu.org

This is a good starting point for all (GNU)Emacs related questions

GNU-Emacs for Win

Goeffs NT-Emacs FAQ

Having worked with Emacs on NT most of the time, this is one of my favourites, it handles nearly all topics of interest concerning Emacs on the M$ platform.
You'll find a lot of links to other sites and packages which are helpful.

NT Emacs Installation by Charles Curley

A page on how to set up Emacs on NT (in addition to Goeffs FAQ) with useful hints and code snippets.

XEmacs

XEmacs: The next generation of Emacs

A good starting point for all these XEmacs users.

Kampis XEmacs Corner

A bright light at the horizon for people looking for a german language introduction to XEmacs

All Emacs

Jari's Emacs homepage

This page holds a big bunch of Emacs related information and interesting links. Jaris page is one of the best sources of information concerning Emacs available on the web. You'll find almost everything concerning any flavour of Emacs on this page.

The Emacs wiki

A wiki trying to collect the knowledge of the Emacs community to serve as a source of answers to all kind of questions concerning Emacs.

The ODP Emacs page

The ODP category for Emacs.

Packages

Emacs Lisp List

Sombody else stated: it's Emacs, so it has to be a list :)
A comprehensive list of Emacs packages (most of them are not part of the standard Emacs distributions).

The ODP Emacs Lisp page

The ODP category for Emacs Lisp.

The cc-mode home

Guess what :)

JDE homepage

This is a must if you are doing java development with Emacs.

The auctex package

TeXing with Emacs ? Give it a try, you won't regret it !

Emacs Goodies at Python.org

You'll find Python-mode there

Alex Schroeders Emacs page

Among other things you'll find additions to his sql-mode there

The VM homepage

A very good alternative to rmail

gnus.org

Home of the MGO Team, the official maintainers of the Gnus FAQ. Provides a lot of stuff about the ultimate News and Mailreader for Emacs.

HTML Helper Mode

The major mode all these pages have been written with

The Insidious Big Brother Database

A contact management utility for use with Emacs.

Noah Friedmans Emacs Lisp

A collection of major and minor modes, user interface enhancements, and library routines for GNU Emacs and XEmacs.

Eric Ludlams contributions to Emacs

The newest versions of speedbar and the packages which are not yet part of the standard distribution. Some of them are needed to use the current jde release.

If you are interested in customization via dotfiles besides Emacs you might want to take a look at the following sites:

dotfiles.com

This is a collection of dotfiles for Emacs and other programs. (Most of the .emacs files are available here in a newer version)

The Dotfile Generator

This is a template based generator for dotfiles. Older versions included Emacs support, but it seems as if Jesper has decided to remove it.