S4: Lost Caverns of Tsojcanth is the name of that module. Along with its companion module, WG4: Forgotten Temple of Tharizdun, it makes for a nice minicampaign.
S3: Expedition to the Barrier Peaks is a long-time favorite of mine. Cool combo of scifi and fantasy, and opens up the possibiltiy of even more. Dovetail this with the 2e boxed adventure Tale of the Comet and it becomes a bit more epic in scale.
Q1: Queen of the Demonweb Pits is another long-time favorite. Gave us the creeps back when we played it more than 20 years ago. Plus, it has a bunch of adventure hooks for excursions into other planes and alternate dimensions.
Temple of Elemental Evil
Desert of Desolation
Ravenloft
Ruins of Adventure (sure, it was based on a computer game, but it was an entire campaign in a relatively small-sized book. The adventures were good too).
White Plume Mountain is nice because it is puzzle-based.
HOWEVER, the puzzles are pretty damn easy... we've been cakewalking the puzzles but the fights have been pretty intense.
I'm not fond of the Giants / Depths / Demonweb series myself.
Lost Cavern of Tsojcanth is cool, big, can be deadly and includes minor puzzles - however it is illogical and sometimes TOO big.
Ravenloft (the original) is awesome.
The last module in the Desert of Desolation set was GREAT. Lost Tomb of Martek. The rest of the set I can take or leave.
X1 and B2 are always going to be two of my faves. B2 Because I ran it well over a dozen times, X1 because it maintains its feel of strangeness to this day - I ran my first 3.0 campaign through X1 even, and the players loved it.
I would have to admit that I3-5 The Desert of Desolation (the compilation, with all the extras) and (A1-4) The Scourge of the Slave Lords are amongst the most successful adventures I have ever had the pleasure to run. They both have a lot of great classic D&D elements, plenty of trap-laden, monster-heavy "dungeons", and great roleplaying opportunities. The Desert also includes a heavy dosage of "problem-solving". Especially good if you're fond of long, complex adventures.