Parallax effect Github 404 was the best. I even had a coffee mug of the design they officially sold (with the text to the effect of 'This isn't the drink you're looking for') but someone took it and they no longer sell them, which was very disappointing.

Wow, yeah. I hadn't seen a GitHub 404 page in a while (new job, don't code much anymore) and my first thought on seeing it was that the 404 page was broken. That would have been an odd recursion.