Internet Easter Eggs

According to WikiPedia, an Easter Egg is: "an intentional inside joke, hidden message, or feature in a work such as a computer program, movie, book, or crossword. According to game designer Warren Robinett, the term was coined at Atari by personnel who were alerted to the presence of a secret message which had been hidden by Robinett in his already widely distributed game, Adventure. The name has been said to evoke the idea of a traditional Easter egg hunt."

Easter Eggs are not limited to applications, movies, etc.  Web sites have them too, some of the best and most documented ones that I have found are in Google and its related properties (such as: YouTube, etc).

I will admit that some of these are better then others, because some are real Easter Eggs while others are 'quasi' features (or something like that).

YouTube

• In the search field, type "fibonacci". (arranges the results in a tiled effect in accordance with the mathematical sequence)
• In the search field, type "beam me up scotty". (the videos on the results page will be ‘beamed’ down)
• Click on a blank part of the page and type "1980" to play Missile Command
• Click on a blank part of the page and type "1337" to see all the comments in leetspeak.
• In the search field, type "do the harlem shake" and press the search button.
• Watch the "Swedish Chef makes Popcorn Shrimp (video)", turn on the CC (closed caption), then select "Swedish-Chef".  You will have to wait for it, it happens about the middle of the video.

Google

• In the search field, type "recursion" (this one is subtle)
• In the search field, type "zerg rush".
• In the search field, type "do a barrel roll".
• In the search field, type "2*sqrt(-abs(abs(x)-1)*abs(3-abs(x))/((abs(x)-1)*(3-abs(x))))(1+abs(abs(x)-3)/(abs(x)-3))sqrt(1-(x/7)^2)+(5+0.97(abs(x-.5)+abs(x+.5))-3(abs(x-.75)+abs(x+.75)))(1+abs(1-abs(x))/(1-abs(x))),-3sqrt(1-(x/7)^2)sqrt(abs(abs(x)-4)/(abs(x)-4)),abs(x/2)-0.0913722(x^2)-3+sqrt(1-(abs(abs(x)-2)-1)^2),(2.71052+(1.5-.5abs(x))-1.35526sqrt(4-(abs(x)-1)^2))sqrt(abs(abs(x)-1)/(abs(x)-1))+0.9"
• In the search field, type "askew" or "tilt" (look towards the top of the page)
• In the search field, type "anagram" or "define anagram" (this one is subtle)
• In the search field, type "binary" (this one is subtle)
• In the search field, type "conway's game of life" (look to the right part of the screen)
• In the search field, type "bacon number [actor's name]" (e.g. kevin bacon, which is equal to 0)
• In the image search field, type "atari breakout"
• Google in different languages:
• Elmer Fudd
• Hacker (Leetspeak)
• Klingon 
• Pig Latin
• Pirate
• Swedish Chef (Muppets)

Mozilla Firefox

• Type "about:robots" in the address bar at the top of the browser window. (Bonus: do not press the button)
• Type "about:mozilla" in the address bar at the top of the browser window.  (history/folklore: its supposed to be a response to a blue screen of death in Internet Explorer 5.5 when “about:mozilla” was typed. )

Google Chrome

• Type "about:crash" in the address bar at the top of the browser window.  It's really nothing more then a crash page in Chrome, but did you know it was there?

Wikipedia

• Go to Easter Egg entry in the pictures of the rabbits click on the little thing that looks like a turtle in the lower right corner.

Note: All of these were tested at the time of the article, but over time some of the features may stop working or be removed.