Ok there are funny things in games you might not notice. Some times a company might put characters or items from one game into another game.

For example in the town of Lahn in Xenogears you get to talk to Luca from Chrono Trigger!

In FF7 when Cloud gets poisoned he sais "Zenogais"

And Xenosaga is FULL of Xenogears easter eggs throughout the series.... Like Jin Uzuki being the nice version of Citian Uzuki!

Citan: The doctor living outside of town with a hidden millitary past that also knows how to use a sword.
Jin : The doctor/librarian living outside of town with a millitary past that knows how to use a sword.
Only difference is that Jin is nice and his millitary past isn't such a secret. Also in Xenosaga 3 the creators decided to dress Jin up JUST like Citan without the glasses.

Xenosaga 1 there is a little easter egg (never found this btw but it's supposed to be there) that Jr. meets up with Big Joe from Xenogears. Also in same game Nifflehiem wears the same pendant Fei wears in Xenogears and it has the same ping noise!

Now my question is have you found any easter eggs in your favorite games?

Many Easter Eggs I have found, some weird, some funny, some even gives the game a rumor in it's plot (Events in the game questioned by easter eggs).

I don 't know many Easter Eggs I found alone, but some I found though the Internet are pretty neat.

One of my favorite ones is the Chell Potato in Portal 2 .

Least Favorite one is the easter egg in Spore which you get for spinning the Galaxy, the developers faces coming out just makes me feel awkward

There are some in Super Smash Bros Melee in the Trophies themselves. If you zoom in on the Metroid trophy and look at the reflection while moving it around you'll see an elevator from Super Metroid. If you look at the reflection for the Metal Mario trophy you'll see a house and the front yard of it.

One of my favorites is in Ocarina of Time. When you first reach Zelda, go left or right to one of the windows instead of going straight ahead to her. If you look through the windows you can see pictures of characters like Mario, Yoshi, Peach, and Bowser.

i think in Metal Gear if you beat one of the levels in a certain time the marines will be in their underwear
and in kingdom hearts if you step on the scale in traverse town it will move

hackerman : there are a ton in mgs4 that iv only just encountered, you can get the assasins creed outfit for snake.
if you knock over a certain picture theres a picture of a famous japanese model behind it(a proper photo)and if you look at the roof theres a massive photo of her.
theres also photos depicting the entire life of jesus christ.
if you go 3 minutes without killing the beauty bosses you get transported to an endless white room, if you pull the camera out they start posing for you.

there was a good one in hitman blood money where if you shot a secret switch everyone ran up to you in there boxers and started applauding you.there was one on a ship where you could make everyone turn into zombies.you ould pick up a keycard to get into a secret room, where mice were having a boxing match, drinking beers, or smoking full size cigars while playing cards.there were also pictures of him in one level.
i shot all the mice in my hideout and got the message "you sent all the mice to there happy place in 22 seconds"

thenumberone : well you can't know every Easter egg but the underwear thing is pretty funny

One time I found a easter egg in Sands of Destruction! I found it was pretty odd...

Snowdeath : Do you mind telling us what the easter egg was?  Or would it spoil the game too much?

Well, for Sands of Destruction, it'd be spoiling the game, but I do have a link for the other easter egg I found on my game, Runescape. It's my favorite one!

http://runescape.wikia.com/wiki/Ferret_of_Doom

One Easter Egg I always liked was in Metal Gear Solid 1.  I feel the whole fight with Psycho Mantis was one.  He did everything from make your controller move to read your memory card.  He referenced some games, and had some designers of Metal Gear on the pictures, which were laughing creepily.  That whole franchise is filled with great Easter Eggs.