3. Gears of War 3 - Gigantic Fire-Breathing Golden Chicken
American game developers can include some ridiculous easter eggs, too. It's safe to say that you don't have to be a Gears of War fan to see why a monstrous golden chicken doesn't exactly fit in with the environment. ...Actually, if you can think of a game where this sort of thing actually DOES make sense, then you have a better imagination than I.
Anyway, if the player shouts into four drainpipes around the level, a giant, golden fire-breathing chicken emerges from the pipes and begins clucking up everything (hyuck hyuck). Does that make sense to you? Me neither.
2. Metal Gear Solid 3 - Snake's Vampire Dream
If you know anything about the Metal Gear series, you know that each game is rife with tongue-in-cheek references, breaks in the 4th wall, and other treats for eagle-eyed players. In terms of its content and position within MGS3, "Snake's Dream" takes the cake in terms of unbelievable easter eggs within the Metal Gear universe. Basically, Snake gets kidnapped and thrown in a prison cell. If the player immediately saves and quits the game, when the save is loaded, the player is transported to a totally different environment. The game transforms into a old school hack-and-slasher, complete with a totally different control scheme, gameplay, abilities, and enemies. They player is free to decimate hordes of zombies to their heart's content. Afterwards, MGS3 proper picks back up as if nothing even happened.