Background Resources:
1. Wikipedia explains Massive Multiplayer Games (eng):
http://en.wikipedia.org/wiki/MMORPG
2. Wikipedia explains Massive Multiplayer Games (de):
http://de.wikipedia.org/wiki/MMORPG
3. Professor Edward Castronova about MMOG issues (eng):
http://mypage.iu.edu/~castro/
4. Different charts and analysis of the MMOG markets (eng):
http://www.mmogchart.com/
5. Player research is provided in the Daedalus Project (eng):
http://www.nickyee.com/daedalus/
6. A rough cut through the history of online games (eng):
http://archive.gamespy.com/amdmmog/
7. Degree dissertation about online gaming (de):
http://www.mmorpg-research.de/
8. Swedish Massive Multiplayer Game Researcher (eng):
http://www.zackariasson.com/
9. Game Research (eng):
http://www.game-research.com/
10. Game Studies (eng):
http://www.gamestudies.org/
11. Online Data About Online Games at VOIG (eng):
http://www.mmogdata.com/

Knowledge:
12. Terms and acronyms explained on Wikipedia (eng):
http://en.wikipedia.org/wiki/MMORPG_terms_and_acronyms
13. Terms and acronyms explained on Wikipedia (de):
http://de.wikipedia.org/wiki/MMORPG-Jargon
14. MMOGlossary.com (eng):
http://www.mmoglossary.com/

Informational Articles:
15. The history of Online-RPGs (de):
http://www.mmplay.de/index.php?seite=snews&tid=239
16. Wage slaves (eng):
http://www.1up.com/do/feature?cId=3141815
17. James Cameron's Game Theory (eng):
http://www.businessweek.com/magazine/content/06_07/b3971073.htm
18. Are virtual worlds the best place to study the real one? (eng):
http://www.walrusmagazine.com/04/05/06/1929205.shtml
19. Sarcastic stories of the daily life in Everquest (eng):
http://eqdailygrind.blogspot.com/
20. The Role of the Everyday User in the Evolution of MMORPGs (eng):
http://www.driftreality.com/london/mmorpg.1.html

Massive Multiplayer Print Magazines and eZines:
http://www.gamerzines.com/mmozine/
http://www.massive-magazine.com/
http://www.beckett.com/beckettMOG/

MMOBLOGS:
Tobold's Blog
QJ.net
Raph's Website
MMODump
Keen And Graev's Gaming Blog
Broken Toys (by Lum the Mad)
WOW Insider
PlayNoEvil Game Security News & Analysis
Terra Nova - Exploring Virtual Worlds
MMORPGblogs

Massive Multiplayer Game Listings :
http://www.mpogl.com/
http://www.onrpg.com/
http://mmolist.blogspot.com/

Tools, Mods, Interfaces, Utilities for online games:
http://www.ogaming.com/data/3467~MMOInterfaces.php
http://www.screamingbee.com/
http://www.mmoger.com/
http://www.goteamspeak.com/
http://www.fraps.com/

Item, Spell, Quest, NPC - Database:
http://www.ogaming.com/data/3468~MMOGameDatabases.php

Beta Testing And Free Online Game Betas:
http://www.betawatcher.com/

MMO Server Emulators:
http://www.shardwire.org/
http://www.eqemulator.net/
http://dol.psykonikcorp.net/
http://www.l2jserver.com/

MMO Currency Converter:
http://www.gameusd.com/

MMO Patches And Files:
http://www.mmofiles.com/

Industry News:
http://www.escapistmagazine.com/
http://www.corpnews.com/
http://mmorpg.qj.net/
http://www.walkering.com/walkerings/
http://www.f13.net/
http://www.gamesetwatch.com/
http://www.gamespress.com/

Organizations And Conferences:
http://www.nogold.org/
Indie MMO Game Developers Conference

News And Communities For Massive Multiplayer Games:
MMORPG.com (eng)
http://www.mmorpg.com/
MMORPGdot @ RPGdot / Jolt Online Gaming (eng)
http://www.mmorpgdot.com/
MMOReports.com (eng)
http://www.mmoreports.com
MYSTICS NETWORK (de)
http://www.mystics.de/
MondesPersistant.com (fr)
http://www.mondespersistants.com/
Jeux Online (fr)
http://www.jeuxonline.info/
STRATICS Network (eng)
http://www.stratics.com/
WARCRY Network (eng)
http://www.warcry.com/
IGN Network (eng)
http://www.ign.com/
Ten Ton Hammer - Life is a game (eng)
http://www.tentonhammer.com/
MMHell (eng)
http://www.mmhell.com/
Griefers dot net (eng)
http://www.griefers.net/
Allakhazam (eng)
http://www.allakhazam.com/
CaosRealm MMOG (es)
http://www.caosrealm.com/
Allvatar (de)
http://www.allvatar.com/
NotAddicted.com (eng)
http://www.notaddicted.com/
Gamebunny - tasty online games news (eng)
http://www.gamebunny.com/
Olnigg (de)
http://www.olnigg.de/
MMOG-Welten (de)
http://www.mmog-welten.de/
MMORPG.pl (pl)
http://www.mmorpg.pl/
The MMO Gamer (eng)
http://www.mmo-gamer.com/
Massively (eng)
http://www.massively.com/
Worlds Away - European MMORPG Community (eng)
http://www.mmorpg.org.uk
MMOABC (eng)
http://www.mmoabc.com/
arenammo (br / pt)
http://www.arenammo.com.br/
MMORPGItalia (it)
http://www.mmorpgitalia.it/
juega en red (es)
http://www.juegaenred.com/

Play Service And Leveling Sites:
http://www.ingamezone.com/
http://www.ige.com/
http://www.rpgway.com/
http://www.swagvault.com/
http://www.offgamers.com/
http://www.team-vip.com/
http://www.mysupersales.com/
http://www.power4game.com/
http://www.guy4game.com/
http://www.igamecurrency.com/
http://www.thsale.com/
http://www.itemgarden.com/
http://www.wowgoldnet.com/
http://www.oforu.com/

Game Secrets, Exploits, Hacks and Cheats:
http://www.surpremex.net/
http://www.sharpplay.com/
http://www.tault.com/
http://www.game-secrets.com/
ElitePvPers (de/eng)
MMOcheats
SiteMagik.com
MMOverload

Online Games Development And Game Design:
Gamasutra MMORPG articles
Gamasutra MMOG articles
IGDA Online Games Forum
Gamedev.org MMOG Programming Forum
Zen of Design (MMOG design blog)
Raph's Website (Blog of Senior MMOG Dev Raph Koster)
Fine Game Design (Blog of David Kennerly)
Massively Multi-Player Game Development (Blog)
Nerfbat (Blog)
Darniaq: Verbosity Unleashed (Blog)
GameProducer.net