Games

Board Games

Chess
Settlers of Katan
Robo Ralley

CCG (Collectable Card Games)

MTG - Magic, The Gathering
Spellfire

Fighting

Mortal Combat
Tekken

FPS (First Person Shooters)

Quake
Team Fortress
Unreal Tournament

MMORPG (Massive Multiplayer Online Role Playing Games)

DDO - Dungeons and Dragons Online
EQ - Everquest
LOTRO - Lord of the Rings Online
MMO Characters
Realm of the Titans from Aria Games
Requiem: Bloodymare
WOKF - World of Kung Fu
Wow - World of Warcraft
Zu Online

RPG (Role Playing Games)

BRP (basic role playing)
Cthulhutech
d20 Modern
DnD (dungeons and dragons)
Gurps (generic universal role playing system)
Gore (generic old-school role-playing engine)
Kiss (keep it simple system)
Overview of tabletop roleplaying games

RTS (Real Time Strategy)

Dungeon Keeper. The original game is still the best of these.

Sandbox

Minecraft