I recently purchased Civ IV. It’s a great auld game, ironing out many of the flaws that I found irritating in Civ III. Anyway, the Celtic Empire civ in the Warlords version has the nice touch of the units all speaking in Irish (gaelic). Not that the celts spoke this language in any modern form at least but I thought it was a really nice touch, especially considering only a small number of players would realise the units are speaking as gaeilge.
•The “bunker” background noises in DEFCON. From shoes squeaking in a corridor, to soft, muted sobbing, to one of the most eerie bit, a man’s distorted voice over an intercom…which, as I found out after opening the sounds file, is actually someone reciting the Lord’s Prayer.
•The AC-130’s aircrew chatter in Call of Duty 4.
•In the original Call of Duty, the notes pinned to the pier at Stalingrad. 
•I’ve mentioned my old, all-time favorite from SoFII before, where a gunshot through a plate-glass window missed a henchman, but left him walking around with a bloody torso (and head) studded with shards of broken glass.
All the Civs speak their native language, which is one of the many great little touches in the game.
Personally, I loved the eminently self-aware OOC stuff your character says in Fallout 2; like mentioning how he randomly goes into stores and goes through stuff just for the hell of it.
In Silent Hunter IV, when you torpedo a ship, you’ll often see lifeboats launch as the ship goes under, and there’s countless ways a ship can sink. Sometimes they break in half, other times they capsize, sometimes they go down stern first… you could almost rename the game Sinking Ship Simulator…
[QUOTE=Martini Enfield}In Silent Hunter IV, when you torpedo a ship, you’ll often see lifeboats launch as the ship goes under, and there’s countless ways a ship can sink. Sometimes they break in half, other times they capsize, sometimes they go down stern first… you could almost rename the game Sinking Ship Simulator…[/QUOTE]
Ah that reminds me, I digress from the OP, of one of my greatest gaming successes ever, it was in an old sub game.
The was a while ago, so clipping and collision detection wern’t anywhere near as good as today, and games just didn’t have quite the team of people to try to think of every occurance and code it in.
1944, I’m patroling off Okinawa, suddenly I see one of the juciest convovs I had ever seen. Tankers, troop carriers, cargo ships, and more. And only 3 destroyers at the very back, leaving the front way exposed. I pounced like a lion Putting toperdo after torpedo into ships, an occasionally my deck gun after I had to surface with spent batteries. The destroyer’s were closing and had gotten in some lucky shots with their guns, damaging suddenly and heavily. Visibility was bad so I started to make a run for it to hide.
Suddenly as I round a coastline I am face to face with a destroyer, I guess the front escort had gotten out of position and wanted blood now. No time to turn(and little ability because of damage) I unloaded all my bow torps and dove. Just before I lowered the scope, I saw my torps had cored him bow to stern. I popped back to the surface to regain full speed. Oh no, another Destroyer right in front. Well actually the top half of a destroyer, maybe the top fourth, now just towers. One of my following torps had apparently gone right through the hole in the first one and blew the bow off of the second Destroyer, causing him to sink just in time for me to surface over him. But no time to gloat, a third destroyer in line, just a few hundred yards back. I had no torps in the tube so I just dove again praying, and his guns hit me square before I was under. I was taking water bad and had to get to the surface, cutting it as close I could under him, and popping back up again. He apparently didn’t have any charges ready for such a suicide move, and I made it under and up. Noticing I had stern torps ready I launched. Two direct hits, he wasn’t going to make it 
Between the smoke and chaos and the original fog I guess the original persuing escorts had lost me. I limped back home for repairs(thank god for the time compress button, it took 5 months), after sinking 600,000 tons of ships and three destroyers in a suicide slalom in the verticle plane.
No realistic sub simulator will ever be that fun 
They might have split up or they might have capsized
They may have broke deep and took water
And all that remains is the faces and the names
Of the wives and the sons and the daughters.
I don’t know that I would call it a “little” touch so much as possibly under-appreciated: the scope of the detail of Grand Theft Auto IV still amazes me.
Now, I know they use sophisticated tools that make copying/pasting of many of the buildings and elements less tedious, but I’m still amazed at just how many unique buildings there are, and around and behind each one is a realistic assortment of trash, trash cans, debris, and riff-raff. Everything except pigeons.
Well…pigeons…and cowbell.