One thing that makes me alternately sad and thrilled is when I use the Wayback Machine to try to recover Greyhawk material no longer actively online. On one hand, I'm bummed because it these items are no longer easily accessible or at least visible, but on the other hand, its like going on a treasure hunt.
Here's an example of a few I've found:
History of Oerth
List of Greyhawk Mini Figs
Temple of Elemental Evil PC Site
Old AOL page (some articles from the Masters linked here)
An Old Campaign Homepage
Using the Wayback Machine is not only fun, but can be an amusing look back at what folks thought about the hobby, circa 1995-2000. We have agonizing over TSR pulling support for Greyhawk, rejoicing at it coming back, bitter partisanship over changes and pigeonholing for Living Greyhawk/3e, and everything else we've come to enjoy in this fine hobby.
The Wayback Machine is sort of like a dungeon delve, isn't it? Maybe that's why I enjoy it so much.