GTR2 - THE racing simulator with a big online community with loads of free downloadable goodies. the only game that I can and do sit down adn do a 24 hour race in real time over the course of about 2 weeks Also still play the original The Settlers game. No idea why but I can still play it for hours.
Halo 2 multiplayer online was awesome, and still play c&c generals all the time, its Forza 2 I'm playing now though
Rebel Star Raiders. Elite Ultima Online Carrier Command BattleField 2 Interstate 76 Far too many too pick a favouite.
COD4 - might be short in single player, but still best game i've played. goldeneye is a classic as well mind, and gta3 was mind blowing when it came out
I`ve recently got COD4 and was a bit disppointed to have completed it in about 5 hours. But online? Immense! The whole GTA series is my favourite of the console era (eagerly anticipating GTA IV). But from back in the day some of the games on my Amstrad 464 provided hours of fun. In no particular order; The Dizzy series Harrier Attack Willow Pattern Arkanoid Stealth Bomber Bomberman and literally hundreds of others, that I can`t remember the names of.
I have a few favorites from over the years.... Streetfighter 2 Streets of Rage (any of the three) Alien Vs Preditor Super Mario Kart Driver Golden Eye Call of Duty (any of them, they have all been great games imo) GTA San Andreas There are definately others, i just cant think of them right now...
The Getaway, but I'm positively c**p at it. Most fun is hooning around London in a bright orange Jensen Interceptor, seeing how many Fuzz/Yardies/Triads you can outrun...