pipe bombing friend

when he came to investigate duke 3d hologram

Beating Wolfenstein 3-D.

Making my first level for Doom 2.

Playing modem-to-modem co-op in Doom 2.

Playing modem-to-modem in GTA1, and organizing head-on collisions between firetrucks from across the map, and then having a shootout.

Beating X-COM for the first time.

Playing StarCraft Brood War for a million years straight.

Solving any puzzle in Day of the Tentacle.

Homeworld. That games is the shit.

Winning the grand campaign in Rome: Total War. Another one was when I had a cool zeal paladin who could tank really well and even though it took a while before he could take out a huge crowd surrounding him, it was cool that he would be able to survive it.

Another epic moment I had was in TFC. I was a sniper in 2fort and there were multiple medics/scouts concussion grenade jumping. I was zoomed in when I saw a medic shoot sky high from the water and in a quick moment, I unzoomed, moved my crosshairs, and headshot him as he was decending at full speed onto the battlements close to where he was about to land. Similarly, playing rounds in Counter-Strike with 8 to 9 kills is a pretty epic feeling.

Yes, Homeworld 1 and 2 were crazy.

Any moment in the Baldurs Gate series

The moment in knights of the old republic when you find out that your raven the sith lord.

Homeworld 1,2 missions
Fallout 2 near the ending
Creating a successful metropolis in Sim City 2000 (C'mon, my first PC game )
Warcraft 3, Patricide cutscene 0_0
SWG. Finding out the identity of a local, very popular cantina dancer. Let's just say man boobs and hair. Lots of it.

Baldur's Gate character exchanges were very memorable.

All of Privateer and most of Freelancer
Mechwarrior 2 and Starsiege online
The insane amount of time I spent on Betrayal at Krondor
PLANESAPE: TORMENT
Battlefield 2 for reintroducing me to the fun of online gaming
The first time I played Half Life 2

Honestly, UT2004 had some of the most white-knuckle moments where it came down to the last second. Any time I got that one last point I needed to win a few seconds before the time is up. I just dont get the same feeling from any other game...

I also rememebr the day I poped Diablo2:LoD CD in my drive and watched that opening cinematic. That was EPIC.

Ultima online for sure, it was fantastic in its prime. It's just hard to pick just one noteworthy moment from it though.