My favourite: http://11111111111111111111111111111111111111111111111111111...

(don't miss the "enter" button)

A more modern work in the same vein: http://tane.us/

The site for the film Requiem For a Dream was always one of my favorites. It was still online as of a couple years ago but appears to finally be gone. But thankfully here's an archive:

http://archive.hi-res.net/requiem/

Seems like this was before my time. What exactly am I looking at here?

Also https://web.archive.org/web/*/http://absurd.org