I would imagine that pretty much everyone is familiar with the Google Doodle. The Google Doodle is when Google swap out their regular logo on their homepage and show a special, stylised version to commemorate a historic event, a famous birth, a national holiday etc. The doodle can be different in different countries or they can be global doodles.
Some of the most recent ones are above: Father's Day, the Lunar Eclipse, Les Paul's 96th Birthday and Martha Graham's 117th Birthday.
My favourite, however, is the one that I can see today. I say 'I' as unless you happen to share the same birthday as me, you won't be seeing this. This is the Google Doodle that Google display to you on your birthday:
In my humble opinion, this is very cool.