Wired magazine, part of Conde Nast, revealed its blacked-out headlines when visitors hovered over them.
The Oatmeal, the popular site where Matthew Inman posts his comics, played an animation putting the argument against the bills in colorful terms. It compared SOPA's anti-provisions to going after kittens with a flamethrower.
WordPress imagined all its blogs, censored. Clicking led to an anti-SOPA site.
Wikipedia, the highest-profile protester, gave visitors information on how to contact their representatives in Congress.
Reddit, another unit of Conde Nast, offered video, frequently asked questions, a petition, important dates and a mechanism to call visitors' representatives.
Minecraft, the big independent video game, just provided a slogan and a link.
McSweeney's, the literary website from Dave Eggers, came up with "a day's worth of facts to get you through Wikipedia's 24-hour blackout," including No. 2, "A whale is a mammal, not a fish." Also: "An old form of broom was the besom, which was made simply of twigs tied to a handle, and was relatively inefficient as a cleaning implement."
And I Can Has Cheezburger, home of lolcats and other funny stuff, posted a pop-up leading to more information and contact information for senators, but allowed visitors to say "No, Thanks" and proceed to the site.