Google is doing a different doodle each day that can be found on it’s main page. Daily it will change to the next version.
View them all here as they are released, or check back daily for the doodle of the day. Last year’s Holiday Doodles can be found here.
Yahoo has an little flash logo that they have updated for the holidays as well. Check out the animated version on Yahoo.com (but I don’t recommend you do anything else there).