If we had a graphic designer on staff, we'd probably have redesigned the whole site for you today with a pumpkin theme. As it is, here are a noticed both YouTube and Google changed logos. If anyone notices any more today, leave a comment and I'll compile them here.
Also after the jump, the last 7 years of Google Halloween logos...
UPDATE



The Yahoo homepage changed too.
The Neatorama guys have spooked up their page a little along with College Humor.
PopCandy, too
bustedtees.
Technorati has replaced their o with a pumpkin.
Ask's page has changed too :)
Mashable has a list of a bunch of them.
Zappos.com is "Powered by Halloween" today.
www.kongregate.com
iwon.com with the pumpkin 'o'