For what it's worth, I've managed to gather a collection of ~10000 fine art images, all legit content all more than old enough to avoid any copyright claims. Problems serving a fileset of this size aside, it generates ~1GB/day (~1000 downloads/day) of interest

Other types of legit content that might be interesting could be:

• Abandonware - web sites hosting abandonware often have problems paying for bandwidth.
• Movie trailers - distribution is generally encouraged, although many web sites insist on playing in browsers rather than allowing a clean download.
• Demo tracks from new bands - lots of these on the web, distribution is welcome, but they can be hard to locate.
• Gutenberg documents - This project aims to preserve 'classic' works of literature (ie, ex copyright) in standard ASCII format.