Tomb of Horrors
One of my earliest role-playing experiences was playing good old first edition AD&D with my brother way back in the early eighties. Dungeon Module S1: Tomb of Horrors was one of the first modules I had seen, and I thought it was the coolest thing ever. There were these great illustrations of the various traps throughout the module, like the mosaic floor, the carved demon's head whose mouth was a Sphere of Annihilation, and the skeleton with a pair of scimitars that sprung out of a chest. After all, that's what D&D was – kill the monsters, get the treasure, avoid the devious traps.
Well, WoTC has updated my favorite module for 3.5 and has posted those very illustrations online. Check it out.