Every holiday google has an altered banner to reflect that holiday. Here are the 3 halloween ones on their server :

http://www.google.com/logos/halloween03.gif
http://www.google.com/logos/halloween02.gif
http://www.google.com/logos/halloween01.gif


Anyone know where more are?

i just found this one too (easter)

http://www.google.com/logos/easter01.gif

http://www.google.com/holidaylogos.html

Google's holiday banners.

http://www.google.com/logos/dilbert_1.gif

http://www.google.com/dilbert2.html

I like this run :P

Google Doodles. :]

Nice
Wonder if one day they will cycle their banner everyday except holidays?