Google is well known for altering its homepage logos to commemorate a special event or Holidays. They have done it since 1999 —at least, that is the earliest documented year.
This year Olympic Games are not an exception. Google Doodle VIII celebrates the 2004 Olympic Games in Athens. Below is a local cache of them (I will keep adding them until the Olympics are over). I hope I will not get into trouble for doing so.
I have changed my mind. To see the Google Doodle VIII, simply go to their Holiday Logos page.