Psion said:
Cordell is a rockin' D&D author with a fertile imagination. What else need be said?
That not everyone agrees with that statement?

I know that after HoNS, my players wanted to corner Cordell in an alley for five minutes and smack him around. HoNS main claim to fame is it's lethality...and while it's no 'Tomb of Horrors' (a module intentionally designed as a DM's revenge on cocky players), of all the Adventure Path modules, it's the most mean-spirited. However, Bruce Cordell is a good author, and I think that the Psionics book alone atones for such sins.
3E classics, to me, will be the same as 1e classics. That is to say, there will be two kinds: the WoodStock modules and the Fishing Story Modules. Woodstock modules are ones that everyone played, or claim to have played. An example is 'Keep on the Borderlands'. Flaws are often forgotten for the nostalgia of yesteryear. Actual quality may not be important towards it's status. For 3E, this will certainly be 'Sunless Citadel' and 'Forge of Fury'. SC was the first WOTC module, and the first real module out after the release of 3E, and many folks (my group included) returned to D&D through this module. FOF is just a good dungeon romp, and was the first chance to take the training wheels off, so to speak. Freeport also falls into this category.
Fishing Story Modules are the ones that generate the best stories to be retold later. 'Tomb of Horrors' definitely clocks in here (although it fits both categories), as do many of the classic modules from 1e, such as 'White Plume Mountain' or 'Queen of the Demonweb Pits', for example. Again, quality isn't necessarily a factor.
What modules do I personally think are 3E classics? The following:
The Sunless Citadel: A good, all-around dungeon romp with plenty of opportunities for characters of every class to contribute. A solid goal, a simple story and plenty of adventure. A well written module well-designed to the task of introducing players and DMs to the new system.
The Forge of Fury: It's not one dungeon, it's five connected ones. A more purely 'old school' crawl, FoF takes things to the next level, introducing a variety of challenges that reward clever thinking, an intelligent design and some classic tropes of the game. There are some problems with the module, but they are fairly minor, by comparison.
NeMoren's Vault: An example of a well-written module with some of the best visual aids to date. Simple and yet elegant, this module is the best of 1e style, coupled with more advanced design sensibilities and a greater emphasis on story and roleplaying. And it has a REAL Umber-Hulk.
The Root of All Evil: IMHO, one of the best modules ever commited to paper. An exciting and rich story, coupled with excellent visual aids and one of the best designs I've ever seen. An excellent start to a series, or easily usable as a stand-alone module. Brilliant stuff.
Of Sound Mind I: Written by our own Piratecat, this is a fantastic module. Simply one of the best modules I've encountered, when it comes to setting a mood. There are excellent DMing tips in the module, an excellent backstory, Claudio Pozas visual aids and a healthy mix of elements for virtually any party. Great, great stuff.
Return to the Temple of Elemental Evil: The Whole Enchilada. A module that becomes a campaign (for a while, anywho), this one is what you make of it. Well detailed, and very customizable, this one isn't just one of the greats, it's a module that can be made to work any way you want it to. There are ample chances for social characters to do their thing, and lots of smack-down to be delivered to the forces of evil. New spells, new monsters (or new to 3E, in some cases) and the most solid tie-in to Greyhawk of any module WOTC has produced for 3E. Never mind the fact that it's written by one of the authors of the Core rules.
YMMV, of course.