Well I searched the word Memorabile and didn't get a hit; so I will start a new thread. What are your most memoabile or favorite gaming moments. I will start with a few - not necessarily in any order:
1) Wizardy I - Proving Grounds - Getting my party utterly stomped on Level 4 Monster Allocation Center
2) EOB I - First time using the stone portal - Wow
3) EOB 2 - Seeming to Kill Dran only to find he turns into a Dragon - Ouch

Need For Speed III - Getting pulled over by a cop and given a light warning as two of his colleagues blazed through the sky overhead and crashed off screen. First time a game made me laugh out loud.
Medieval 2 Total War - Finally getting cannons right at the end of the game and using them against the walls of Jerusalem. The walls came down, bringing many hundreds of soldiers with them.
Portal - Pretty much all of it. Short but very, very sweet. I hope the sequel doesn't go the way of Episode 3.
Unreal Tournament - CTF Face. To those who know, I need say no more.
There are some more. Probably better ones. But those are good for starters.

Planescape Torment: The ending cut-scene. The dystopic-ness of it really made it for me.
My most memorable is one of my earliest:
X-wing: The series of missions in the middle of the game where you take down a crippled Star Destroyer. I remember the last mission where you are escorting the bombers. I was dog-fighting a TIE and had been drawn away from the main fight. I remember seeing the message at the bottom of the screen saying the Star Destroyer was destroyed. I whipped my ship around right in time to watch this massive ship, engulfed in decompression explosions, burst into a massive fireball that filled my entire screen (from 10K away).

All of Mount and Blade.
The opening cutscene and first few minutes before Joker escapes in Arkham Asylum.
All of the Halflife games.
Too many more to name.

Final Fantasy VI (SNES) : after the End of the world, one of my characters (female) is stranded on a small island with an old man an a pig. Litterally there's nothing to do, nothing happens, during several in-game days. I start to think I missed something. Then, the old man and the pig die. The girl is crying, and, not wanted to remain alone, she throws herself from a cliff into the ocean... Boy, this scene got me "WTF ????" as I didn't know that japanese RPG could deal with those quite adult themes.
TES Morrowind : I opened the door of the barrack and... that's it ! The world lies at the threshold, boy ! Got me some minutes to dare adventure myself out of the village, I was so impressed with the implications of that "liberty", mainly that anywhere, anytime, I could run into a far too strong opponent, IRL style! ^_^
Half-Life² Episode 2 : to defend the secret base against the Tripods' attack. Made me really feel at a crossroad between Star Wars and War of the Worlds!
Ultima Underworld : My first 3D game, I litterally spent hours daydreaming in front of the review in a videogames magazine... and I was not disappointed when I got my hands on it!!

Grabbing the Master Sword in A Link To The Past was pretty memorable for me.
There's something genuinely stirring in the way that little clearing in the forest looks. Ah memories! :)

red orchestra: A winter city map on the Russian side. Took position in a bombed out building right next to the germane front line. Held of most of them off until the very end when I almost got killed. I spun around and saw a German aiming a mp-40. Right then, the game ended and I lived.
sven-co-op- Played afraid of monsters campaign. I was in a building basement and lost when I turned around an saw an enemy in front of me, I had to reload in the middle of the fight so I backtracked into a storage room and noticed a zombie near the entrance. I frantically backed into a corner and had to fire one shot and reload to keep them back. I was freaked out and swearing for help while accidentally holding down the voice talk button.
Medal of honor: breakthrough multiplayer demo. It was a map full of ruined apartments and was on the German side using a non-scoped Kar-98k. I was sniping people across the map and getting the highest kill count on the server.
Call of duty UO: The last American level where you have to defend the manor from the tanks and incoming German troops. That level is so hard on hardened and I barely survived in the end. Felt great when I won. Then again, the whole game was memorable compared to the first one.
Call of duty: The Russian level where you have to defend the apartments. All of my allies died and was stuck being prone in a corner just hoping that I don't die. Once the time ended and new allies came, I was so relieved and happy to have made it.

Medal of Honor: Alllied Assault - The Omaha beach level. Probably the most immersive set-pieces in gaming history. The best part about this was that this level was about halfway through the game, so it didn't have to hold the players hand too much. The sounds and atmosphere were just so incredible. I used to boot up this game for my friends just to show them this level.

Fatal Frame III: Hour XI, Kei's finale. [MASSIVE SPOILER!!!!] Kei gets it in his head that he will finish the ritual and impale Reika with the Five Stakes, and makes it to her tomb, if only to discover that the ritual was completed, and she was active. The door shuts behind him, and he is never seen again. [End Spoilers]
The first 10 minutes of HL2
The entirety of Portal
Planescape - Torment: The encounter with Ravel, and the finale. Never have I seen such excellent writing in a game.
The last encounter with Angela in Silent Hill 2 stands out, though I remember the whole game.
Fighting Scarlet in SH5
The railcar ride with Yeesha in the beginning of Myst 4
Warping to the Rebel Base and encountering natives, feeling completely alien in Riven.
The lesbian landlord in The Longest Journey

how has stalker missed this thread?!
ok, so i'm underground, i know there's one of those things with like four lip-tentacles on its face, because i can hear that creepy-ass moan they make when they're near but they haven't spotted you yet. so i'm already on edge. i round a corner and run into a mob of VERY well-equipped mercs. they open fire and drain half my health before i can duck back around the corner, then i realize the mutant has seen me. i sidestep as it lunges which brings us both back into the mercs' views, but this time he takes all the bullets for me. the thing takes down all five of them as i am spraying bullets into it with my automatic. it turns around and comes at me as i run out of bullets, i will die in one hit if it gets to me--i pull out my pistol, fire a shot when it's about two feet away from me and it goes down. i may have pissed my pants.

Diablo - returning to Tristram, the OST is really something to remember.
Diablo II - killing Diablo, Andariel and Baal, exploring the marvellous sets all around the game.
Prince of Persia - The Sands of Time - too many moments to remember, maybe the end of the story told by the prince to Farah...
Out of this World - The end is touching.
Mortal Kombat - heck, it took so much coins to finish the entire game :-P
Severance - Blade of Darkness - the last boss, strange, somewhat challenging and funny.
And many, many more....

Hmm, this whole post will be spoilerific
GTA4:
-The death of Kate McReary at Roman's wedding. I never liked Pegorino before, he was a whining useless bitch who took it from every other mafia family and expected respect but after killing Kate, I actually really hated him.
-The whole museum trilogy in the main game and the DLC
-The Lost And Damned, the whole damned thing
-Luis almost killing Tony in The Ballad Of Gay Tony, not quite sure how that was going to turn out
Freespace 1 & 2:
The Lucifer, The Sathanas, The supernova sequence
Planescape Torment: Most all of it