Hubble Telescope

This April 24, 2010 Google Doodle celebrated the 20th anniversar of the Hubble Telescope.



Barcode

Google honored the anniversary of the invention of the barcode by swapping G-O-O-G-L-E for an image of the barcode (which, if decoded, actually read 'Google.')



NASA

This Google Doodle was featured in honor of the 50th Anniversary of NASA on July 29, 2008.



Tetris

Designed in 2009, this Doodle honored the 25th anniversary of Tetris.


Crop Circle In Honor Of H.G. Wells

A mysterious 'crop circle' Google Doodle appeared on the search engine's homepage. The image gradually evolved, and it took several days for its meaning to become apparent: it marked the anniversary of the birth of famed science fiction author H.G. Wells.


Comic-Con 2009

Google gets geeky and tips hat to Comic-Con (July 23, 2009).

Louis Braille's Birthday

To celebrate Louis Braille's birthday (January 4) Google converted its logo to 2D Braille.



Nikola Tesla's Birthday

A Hungarian-born inventor and engineer, Tesla was one of the important players in the birth of consumer electricity. His birthday is July 10. Fun fact: He is often credited with the concept of a "death ray" gun, a popular sci-fi weapon


Sir Isaac Newton's Birthday

January 4 is the birthday of the 'Father of Physics.' Google honored Sir Newton with a Javascript logo of an apple tree branch that drops fruit when you click. It's Google's first animated Doodle. See a video of the animation at HuffPost Tech.