Big Download, Shacknews and presumably others. Game Videos no longer has the trailers, although other gameplay clips still remain; as of this writing, Game Trailers still has the trailers online. Here's the full email:
In connection with ESRB's advertising guidelines, you are instructed to remove immediately any of our Fallout 3 trailers from your website, pending further notice. Thank you for your attention to this matter.
We're as confused as you are. We've reached out to Bethesda for more information.