MODULE/ADVENTURE - A true classic from the early days, and all-the-better for being aimed at low-level characters. The seemingly innocuous "Village of Hommlet" leads to an overland adventure for the journey to Nulb and then to a pair of sensational dungeon adventures.
Despite its age and incompatibility with the current D&D rulesets, this adventure should be MANDATORY reading for any aspiring DM. It is a textbook on how campaign background (including religion), NPCs, town adventures, overland adventures, and dungeons can all fit together brilliantly. Furthermore the final adventure (Nodes of Elemental Evil) is a case study in how to "mess with the rules for dramatic effect" (lots of well-thought-out spell variations and the like).
Even if you never actually play it, careful study of this module will reap enormous returns. It would well be worth adapting for 3.5/4.0.
SCAN - An excellent scan. The first scanned page (the full colour front cover) shows a bit of physical wear and tear, but everything else (body text and maps) is pristine.
ADVENTURE - 5/5
SCAN - 5/5