Internet

General - Trackers - Samplers - Players - CD-Rippers - Samples - Modules -

Links marked with a * haven't been tested by me.

IRC

These are the various channels that most trackers hang out in:
Most networks - #trax
DALNet - #modulez
irc.scene.org - #trax (you can find me in here when I'm on IRC)

Usenet

alt.binaries.sounds.mods
alt.binaries.sounds.mods.d
alt.binaries.sounds.mods.techno
alt.music.mods

Conversions

Here are the links to all the various conversions of The Tracker's Handbook that are currently available.

http://egnatia.ee.auth.gr/~nalevrid/files/Handbook/Handbook.htm
http://united-trackers.org/resources/handbook/

General

Cools Productions - http://listen.to/cools
United Trackers - http://united-trackers.org/
MAZ Sound Page - http://www.maz-sound.com/
Mod Resource Web - http://www.armory.com/~greebo/mod.html
LOK - http://www.loknet.demon.co.uk/
ModPlug Central Resources - http://www.castlex.com/mods/
Novus's Wide World of MODs - http://surf.to/novus
Temple of MOD - http://egnatia.ee.auth.gr/~nalevrid/
SynthZone - http://www.synthzone.com/
Everything Impulse - http://www.vrone.net/gorenfeld/
AKA's MOD Page - http://www.tu-chemnitz.de/~aka/
a.b.s.m FAQ - http://welcome.to/modfaq

Trackers

Samplers

Cool Edit - http://www.syntrillium.com/
GoldWave - http://www.goldwave.com/
Sound Forge - http://www.sonicfoundry.com/
AWave - http://hem.passagen.se/fmj/fmjsoft.html
AWave is a Win9x program to convert samples. It's shareware, limited to a single convert per run.

Players

MikMod - http://www.stack.nl/~mikmak/mikmod.htm
The Mik range of players covers a wide variety of platforms.

Amiga

Windows 3.1/9x/NT

ModPlug Player (9x/NT) - http://www.castlex.com/modplug/
Mod4Win (3.1/9x/NT) - http://www.mod4win.com/
OctaMEDPlayer (9x/NT) - http://www.octamed.co.uk/

DOS

Cubic Player - http://www.geocities.com/SiliconValley/Vista/4107/
Multi Music Player - http://www.cerise.ml.org/charles/

Mac

Unix/Linux/Sun/NeXT

CD-Rippers

CD2Wav - http://sunny.aha.ru/~gw/
Audiograbber - http://www.audiograbber.com-us.net/

Samples

Soundwave - http://www.volftp.vol.it/soundwave/samples.html
Only go to this site if you are prepared for some LARGE D/Ls.
Hyperreal - http://www.hyperreal.com/
Tons of samples, inc. the complete TR-808 and 909 sets. There is another site, the Drum Samples page, which is missing a lot of the 909 Snares, and the 808 Hi-Conga file is corrupt. I recommend Hyperreal.
SampleNet - http://www.samplenet.co.uk/
FTP Server - ftp.futurenet.co.uk/samplenet/
The WWW site provides all the links to the files on the FTP site, plus descriptions. However, directly accessing the FTP site, whether through a browser or an FTP program (make sure it allows D/L of multiple files and/or directories), is far faster.

Modules

The ModArchive - http://www.modarchive.com/
Trax In Space - http://www.traxinspace.com/
Mod Heaven - http://www.modheaven.com/
If any of the above links are missing or down then contact me so I can remove them. If you have any to add, then send me the category and the URL...