I think demo discs are pretty cool. As I mentioned in a previous entry, they gave us an opportunity to play a game before it was released, as well as give us other useful tidbits and secrets. While high speed internet has pretty much made the demo disc obsolete, I still hold a fondness for them.
Here are most of the demo discs I own:

To me, demo discs are a great snapshot of the video games of old to me. They give people a chance to gleam into what gaming was like in that time period. For instance, look at this menu of a PC Gamer demo disc circa late 1999:

The main menu, as well as some of the pages, have those remnants of late ’90s web design. Completely animated, with varied fonts, a somewhat confusing web interface, even animations everywhere.
On this specific disc, there’s even a gallery of really bad photoshops of former PC Gamer mascot Coconut Monkey in there just to drive it home that this is a byproduct of late 1990s PC gaming culture.

