Although, I'm gonna cut right in line and ask: what's the most interesting thing you've archived? If you're not sure what we'd find interesting, some suggestions are - content, medium and difficulty.
For the most interesting thing, I'll share two answers:
- First, there were the truly historic pieces of media. Things like Thomas Edison's first motion pictures and reporters' wire spool recordings of D-Day hours after the invasion "ended" were always the most amazing. You read about this stuff, but hearing it is something else entirely.
- On the other end of the spectrum, you have to remember that everything that has a registered copyright has been sent to the Library of Congress. That includes porn. My group didn't archive it but the group down the hall had to catalogue it. No, they didn't have private offices. ;)