Google has hidden some fun secrets and easter eggs into their online searching tool. I see some interesting list mentioned in other answers and I found the following list could be an add-on
To find the distance and flights between two cities you just type in the name of two city. This will give you a flight information from source to destination with approximate driving time approximately miles.
Atari breakout - Google made Atari breakout playable on image search . Google for Atari Breakout and select images, wait for a second and you see Atari breakout game loaded on your screen.
Search for Do a barrel roll to see search results doing a barrel roll.
When you don’t have a coin handy type flip a coin into the search bar.
Search for the term “Tic Tac Toe ” to play the game without visiting any link.