I can’t remember Google ever having a special “doodle” or logo for Pi Day, but that has changed today, March 14, 2010. If you visit Google.com today, you will see a special logo for Pi Day, which is celebrated by most on 3.14 – as you might understand.
Here is a picture of the logo:
It is also Mother’s Day in the UK with the following logo at google.co.uk:
And the anniversary of Félix Rodríguez de la Fuente, which is represented at google.es today: