1. I6 Ravenloft (TSR 1983) by Tracy and Laura Hickman
Spine-tingly well written and powerfully and potently evocative, this one is easy to recommend. This should have been number one on the Dungeon 30.
2. Red Hand of Doom (WotC 2006) by James Jacob and Rich Baker
This is a new classic. Exciting and cinematic, the players get to decide the course of a fantasy war.
3. D3 Vault of the Drow (TSR 1978) by Gary Gygax
The 'Queen of the Spiders' super-module was ranked number one by Dungeon but really where does the genius in that series lie? Could it be the adventure where you infilitrate the world's most evil city and discover a wonderland of intrigue and evil? Could it be the one set in a subterranean Sodom -- a dark and decadent fairyland -- where drow and daemon freely intermingle? Could it be that one? Or is the adventure where we discover that the Abyss looks like a 70s bath towel?
By the way, someone adapted Vault to Mongoose's Conan and boy does it work!
http://hyboria.xoth.net/adventures/index.htm
4. J1 Entombed with the Pharaohs (Paizo 2007) by Michael Kortes
Another new classic. This is like I3 Pharaoh with the volume turned up to 11. Derivative? Certainly! The genius is incorporating such familiar tropes and still keeping them fresh and exciting.
5. The Age of Worms AP (Paizo 2005-2006 in Dungeon) by Lots O' People
This adventure path is the definitive D&D campaign at last written down, fully fleshed out and placed in Greyhawk. Obviously an act of pure love and concentrated genius. Yes it is a little uneven in places ('Three Face of Evil' anyone?). But its highlights more than correct for it. That and you get to fight Dragotha. Yeehaw!
Gary