Demoscene-Related
Untergrund.net - Our hosting. If not for them, we wouldn't be able to host this stuff properly.
Pouët.net - The biggest forum and demo database. But you do already know about this place, right?
Demozoo - A more sophisticated demo database. It doesn't have all the prods that are on Pouet, but it makes up for it with all the metadata like tags and member info. Really cool!
Scene.org - They got the biggest demoscene-oriented FTP! Also, they host Pouët.net.
The Mod Archive - .mod, .xm, .s3m? They got 'em. Listen to some good tracker music and upload your own!