The Adrenaline Vault
One of the leaders in online gaming magazines, Avault.com is aimed primarily at the action crowd but includes some more general games coverage.

Blue's News
Stephen "Blue" Heaslip's giant PC and console gaming site, which has been a fixture of the gaming community for years.  Constantly updated with up-to-the-minute news about computer and console games, and the gaming hardware required to run it.  An entertaining bonus is the "Link of the Day" feature.

GameSpy
A sprawling network of sites devoted to PC and console gaming, and home to the Daily Victim.

Gone Gold
Rich LaPorte's computer gaming site, dedicated to newly released game titles.  Notable for its capsule reviews of new releases, the "Gold Guide" meta-review index, and Rich's inimitable daily "Roll Call."  Along with Blue's News, one of my two favorite gaming sites.

Cougar World
James "Nutty" Hallows runs the unofficial support site for the Thrustmaster Cougar, the highest fidelity HOTAS (Hands On Throttle And Stick) controllers ever produced for the desktop PC.  Fully programmable with its own advanced scripting language, the Cougar replicates the sidestick and throttle of the Block 50/52 F-16C, and even includes authentic stenciling on its all-metal construction.

Falcon 4.0 Unified Team
Falcon 4.0, released by the now-defunct Microprose in late 1998, was the "mother of all jet sims," the most ambitious effort ever made at simulating modern tactical aviation on a PC.  For various reasons, the Falcon 4.0 series was terminated; however, the enthusiast community picked up the code and began building unbelievable enhancements on top of the Falcon 4.0 engine.  Four years later, Falcon 4.0 with the latest "SuperPAK" enhancement package is barely recognizable.  Visit the official site of this amazing grass-roots effort at building the ultimate F-16 desktop simulator.

Frugal's World of Simulations
Mark "Frugal" Bush runs this fantastic site covering PC combat flight simulations, notable not only for its in-depth coverage of modern flightsims, but also for its series of columns written by flightsim enthusiasts who also happen to be professional aviators by day.  If you want to understand the hobby, you need to visit this site.

GhostRecon.net
Site devoted to Red Storm's Ghost Recon, probably the most realistic first-person tactical shooter on the market today.  Particularly entertaining are the various mods that the community has created for Ghost Recon, including firearms packs that allow you to attach all kinds of exotic SOPMOD attachments to your M4A1 carbine.

Harpoon 4
The latest in the Harpoon series of contemporary naval wargames, which will probably be released sometime next year.  (Hopefully.)

Lock On:  Modern Air Combat
From the makers of the Su-27 Flanker series, LOMAC is a forthcoming modern fighter simulation featuring the O/A-10A Warthog, F-15C "albino" Eagle, several flavors of Su-27, two flavors of MiG-29, and the Su-25.

MiGMan's Flight Sim Museum
MiGMan's site devoted to flightsim nostalgia.  Remember Microprose's original F-15 Strike Eagle, or F-19 Stealth Fighter?

The Pink Flamingo Bar and Grill
Pierre "Papa Doc" Legrand's simulations page, mainly devoted to Flanker (although he appears in recent days to have caught car-sim fever or something...) 

SimHQ.com
An excellent site exclusively devoted to simulations of all kinds, notable for its first-rate news section.  My personal favorite for general simulations coverage.

SUBSIM Review
Neal Stevens runs this web site devoted to reviews of submarine simulations.

Waypoint
Online magazine of the computer Harpoon community, published by Dimitris V. Dranidis.  Generally published on a monthly basis, and with some very substantive content.

Battlefront.com
An independent publisher of wargames, whose notable titles include Major Holdridge's acclaimed TacOps series, and the revolutionary Combat Mission series of 3D tactical games.

The Complete Wargames Handbook (2nd ed.)
This is James Dunnigan's online edition of his well-known wargames guide, which went out of print in 1997. This is a good read for newcomers to modern wargaming, from the perspective of one of its leading designers.

HPS Simulations
Best known for ugly-but-deep grognard games (for many years its flagship offering was the Tigers on the Prowl series).  Published Jim Lunsford's underrated Decisive Action, the modern corps- and division-level game that got its start as a learning tool for CGSC students.  Now publishes a number of very popular John Tiller designs.

The Independent Player's Home Page for Strategy and Wargames
Pascal Ode has assembled a fantastic site with tactical tips, utilities, and FAQs for some of the most popular computer strategy and wargames, including Steel Panthers and Close Combat.

M. Evan Brooks Home Page
M. Evan Brooks is a wargamer (currently assigned to NDU's Wargaming and Simulation Center), software reviewer (CGW's former wargame editor), military professional (currently USARNG), and tax attorney. He has compiled a remarkably broad survey of wargames and war-related computer simulations. Read his Quintessential Wargamer's List, Quintessential Wargamer's List for Military Professionals, and The Worst in Computer Game Advertising. And if nothing there grabs you, you can look at his Guide to Federal Taxation (he also happens to teach two courses on the subject).

Matrix Games
Independent publisher of a number of notable computer strategy and wargames, including projects by Gary Grigsby, "Wild Bill" Wilder, and Simulations Canada.  Matrix has been responsible for the updating and overhaul of several classic wargames, including Grigsby's original Pacific War (which is downloadable for free).  Some interesting projects are in the works, such as Flashpoint Germany.

TacOps 4
The latest version of Major Holdridge's groundbreaking tactical simulation of modern land warfare.

TacOps IRC CPX Page
James Sterrett, umpire extraordinaire of the IRC CPX, runs this comprehensive resource to the TacOps Command Post Exercise, which is a remarkably sophisticated, umpired wargame based on the TacOps engine. Best described as Kriegspiel-meets-the-Internet, CPXs are run on weekends via multiple channels on Internet Relay Chat. The scenarios are inspired and the lessons-learned fascinating. Come read a few of the AARs (After Action Reviews) of previous CPXs archived here, and I guarantee that you'll be intrigued.

Uncommon Valor
Gary Grigsby's acclaimed operational-level portrayal of the South Pacific war, 1942-1943.  A crisp, streamlined interface mated with a sophisticated game engine makes this wargame remarkably addictive.  Manages to place an incredible amount of detail at the player's disposal without reducing play mechanics into a spreadsheet exercise.

Age of Kings Heaven
One of the single most complete resources devoted to Age of Empires II/Age of Kings, including downloadable map scripts, tips and strategies, and recorded replays.

Age of Mythology Heaven
From the creators of the Age of Kings Heaven site, a new online resource for Age of Empires III.

AOM Center
RTSGamer's dedicated Age of Mythology site.  Notable for its download archives.

Mr. Fixit Online
Offering "powertools for gamers," MFO offers tips and strategies for a number of games.  Particularly notable for its coverage of realtime strategy games, and includes some fairly detailed unit analyses for Empire Earth and the Age of Empires series.