Mark CMG
Creative Mountain Games
Red Hand of Doom was certainly a favorite of mine during the last edition era. Freeport (etal) and Witchfire are winners, too. The Whispering Woodwind is my own adventure that has been well received and remembered.
I feel like this idea may have worked better in 1E than 4E. Slogs like this make me suspect the people that wrote the early 4E modules didn't really "get" 4E.5. Keep on the Shadowfell (not widely regarded as awesome, but a TON of exposure, and cleaned up a bit, and available for free now).

Agreed, though I can think of some 3.x modules that come close. For example, I'd include Return to the Temple of Elemental Evil in any such list. For a while there seemed to be quite a few groups playing it and posting on the boards.
No question Paizo has published some great modules and AP's, but I suspect none of them have the market penetration to have a lot of players fondly reminiscing about them 10 years, much less 20 years from now.
- Shackled City - first Dungeon AP, although the links between the mods were tenuous, at best.
- Whispering Cairn - first mod in the second Dungeon AP, Age of Worms. Good on its own; great in how it presages the campaign to come...
- Burnt Offerings - made goblins scary again (or at least made them memorable/notorious again...).
- Stolen Land - first mod in the Kingmaker AP. Early days for this one; it came out in Spring 2010, but I think it will resonate through the ages...
S'pose I should include Ptolus and World's Largest Dungeon. Not my cup of tea, and I never played them; I never bought into the implicit "bigger is better" credo around either of these things. However, they seemed to resonate through the community...
But some of my favorites for 3.X were by Monkeygod, a tiny company without the the distribution to make the list.
The Auld Grump