I hope it's not bad form for a newbie to start a thread, but I'm an easter egg junkie. Thought I'd toss out a few of my favorites and I'd love to see everyone else's. This has been done in here in the past 5 years but those threads didn't seem to get many replies.

Thief (1or2): Dancing Zombies
MOH AA: Dancing Nazis
WarCraft 3: Fight Club
X-Wing: Santa Clause
and my personal favorite
Sacred: Jason Vorhees' gear (usable by the gladiator)

How about a spoiler alert?

Off the top of my head there's:
Anachronox - Dopefish
Little Big Adventure 2 - Time Commando
and Duke Nukem 3D and Shadow Warrior have too many to mention

Ooops, good point. Luckily none of those I mentioned involved any spoilers.

Just mentioning them might be spoilers to some :P

I like the Fallout's phone booth egg ;-)

What about M&M 6's NWC dungeon?

In the GTA games there are plenty of easter eggs: Zombie Elvis newspapers, Rockstar Constellation, references to Scarface or Miami Vice, trash cans containing maps of Vice City, boxes containing articulated figures of Claude Speed and Tommy Vercetty etc

The dancing robot in System Shock 2

Summoning Pyros in Crusader: No Regret

Claptrap in Torchlight II

"That's one dead marine"

Half-Life in San Andreas area 69

And off course - the Easter egg Easter egg

The Dopefish Lives!

I actually used to play a game where you was The Dopefish and swam around, ate things and burped if my memory doesn't deceive me.
I wonder if it's still findable on the net?

Loved it when I found The Dopefish in Quake. :)

In Hitman: Blood Money, the front page of a newspaper lying on a table somewhere contains an article praising Press Play On Tape, a Danish C64 remix band. At least one of the band members worked for IOI at the time.

Mind you, they deserve all the praise they can get. I have all their albums, and go to as many of their concerts as I can.

Every single Easter egg in Borderlands 2
The Halo Covenant dance clubs
The sheep tower defense bonus level of Warcraft 3: Frozen Throne

Great site: http://www.eeggs.com/

Best easter egg ever: http://www.youtube.com/watch?v=yyfswDAZQeU