Favorite Easter Egg in a Game.

[DarthNinja]

On L4D2 when Johnathan Coultans Re:your Brains played on the Jukebox
If you consider than an easter egg

This one gets my vote too.
Another one that isn't exactly a game egg is the 'hidden' steam game "Spacewar":
It's actually a demo app for Steamworks, to install it you have to to use the steam installer url: steam://install/480
Then you can run it from the steam menu, or from steam://run/480

Some pics:
Main menu: http://screencast.com/t/MTBiMDAw
Achievements: http://screencast.com/t/ZTVkMjk2NmY (no, they don't show on your steam profile)
Game: http://screencast.com/t/OTNiZDllM2Y

Hints:
There is no mouse, use arrow keys to navigate the menus.
Gameplay is you and another player(s) fighting to the death while trying to avoid a black hole in the center of the map.

 

[Formica Archonis]

There's probably a lot that I'm forgetting, but a few of my favorites:

1) Tau Ceti: The Lost Star Colony for the C64. In a moment of frustration, I typed something crass, and it told me off for swearing then deliberately ended my game. Of course, my enjoyment was helped slightly by the fact that I'd saved not long before!

2) The Nameless Mod. Oh my heavens, it has tons. My favorites have to be the hidden conversations in the DXI ruins and the various odd things (like the fight with your evil twin Treskton) that unlock that beautiful easter egg of the hidden Narcissus ending.

 

[Anticitizen_Two]

When I found the Lost Easter egg in Half-Life 2: Episode 2, I nerdgasmed.

 

[Dys]

"Sure could use some grenades"

Heh, what halo did well...it did well.

Also Miaq the liar and morrowind in general.

 

[Darth Rahu]

Rodin from Bayonetta saying, "Hey whaddya buyin'? Hehehe, heard that in a game once." EEEEEE!! Resident Evil 4 reference!

 

[Toar]

"Redrum" (Steven King's the Shining) posted in blood on the first Silent Hill (1999). It set the mood when you were running from demon buzzards and hellhouds...

 

[tristow]

the easter egg in vice city

 

[Deef]

The easter bunny in Saints Row 2.

 

[MiracleOfSound]

Fear Factory and Strapping Young Lad lyrics on terminal in Fallout 3

Nine Inch Nails lyrics from a tanker-vagrant in Fallout 2

 

[Audioave10]

Finding Gordon Freeman in Stalker "Shadow Of Chernobyl". One of the best eggs.

 

[DustyDrB]

All I can think of here reacently would be Assasin's Creed 2. When he said, "Its-a me Mario!" I cried I laughed so hard.

I'm with you on this one.

 

[tsb247]

In Operation Flashpoint: Cold War Crisis, all small pine trees will turn into Christmas trees if your system clock is set to December 25.

I thought that was the most clevar easter-egg ever when I found it.

 

[blankedboy]

In Windows XP.

Go to Start>Run.
Type 'telnet'
A box opens, type 'o'
An arrow appears, type 'towel.blinkenlights.nl'

Enjoy ASCII-Mation Star Wars.

 

[Smokeydubbs]

Spoiler

GTA: San Andreas, the Gant Bridge

 

[Composer]

Gotta go with Samus in the swimsuit on this one.

say whaat? this is one i havent heard of.

 

[Sgtkillalot0]

Oh Borderlands how I love thee....

 

[legion431]

Mass Effect 2, when Legion does the robot.

 

[Fox242]

This one hidden message that was behind a fence that was really, really difficult to find in
GTA III. I spend about 2 hours looking for the damn thing and when I finally get to it, the message reads "You weren't supposed to find this." I would have been really upset...had it not been an awesome waste of time!