Charlie Brooks has been a good friend to me for over twenty years, and he ran my first few D&D games. I'm slightly surprised that I haven't linked to his site sooner. I also want to point out that Garyl Shadowslayer is one of my favorite NPCs, though I didn't get to participate in that particular campaign.
There is an excellent post at The Society of Torch, Pole and Rope about running a sandbox campaign focused around preparing to take on The Tomb of Horrors.
The Tomb of Horrors is one of the few modules I own (unless you count my collection of Dungeon magazines), and I rather like this idea. I wonder if I could pull together some people to play this at some point.