I like Mozilla's page the most so far.

Explains SOPA in layman's terms and how it could affect the internet, and a small part about why it was brought up in the first place.

And a pretty big call-to-action button.

If only it was on Facebook.

We are also "blacking out" the default Firefox start page for users in the en-US locale: http://blog.mozilla.com/blog/2012/01/17/mozilla-to-join-tomo...

I don't see anything (connecting from Britain) does anyone from the US have a screenshot? I assume it's US only.

You can see the SOPA page that US people see here:

http://mozilla.org/sopa

Works as usual for me also - I'm in Ukraine

php.net is also black

EDIT: it looks like only the landing page is dark