A1-A4 Scourge of the Slave Lords 20
B1 In Search of the Unknown 20
B2 The Keep on the Borderlands 20
B3 Palace of the Silver Princess 17
B4 The Lost City 20
B5 Horror on the Hill 20
C1 The Hidden Shrine of Tamoachan 20
C2 The Ghost Tower of Inverness 20
D1-D3 Drow 20
EX1-EX2 Dungeonland/Magic Mirror 21
G1-G3 Against the Giants 20
I1 Dweller of the Forbidden City 21
I2 Tomb of the Lizard King 20 I3-I5 Desert of Desolation 21
I6 Ravenloft 21
L1 The Secret of Bone Hill 20
L2 The Assassin's Knot 20 N1 Against the Cult of the Reptile God 14
Q1 Queen of the Demonweb Pits 20
S1 Tomb of Horrors 20
S2 White Plume Mountain 20
S3 Expedition to the Barrier Peaks 17
S4 The Lost Caverns of Tsojcanth 20
T1 Village of Hommlet 20
U1-U3 Saltmarsh Series 20
UK1 Beyond the Crystal Cave 20
UK2 Sentinel 18 -
WG4 Forgotten Temple of Tharizdun 20
X1 Isle of Dread 20
X2 Castle Amber 20
X3 Curse of Xantathos 20
X4-X5 Desert Nomads Series 20
It's every D&D fan's responsibility to research every single one of those on the list as they are a huge part of this game's rich history - even the duff modules (B3 and X3 - which was so bad our thread creator couldn't be bothered to spell its name correctly!!!). Most of the options on the list have a lot going for them though, lots of interesting stories, NPCs and encounters for modern DMs to plunder inspiration from.
Have a browse, read reviews from respected sources (MerricB!), and immerse yourself in a slice of history.
A1-A4 Scourge of the Slave Lords 20
B1 In Search of the Unknown 20
B2 The Keep on the Borderlands 20
B3 Palace of the Silver Princess 17
B4 The Lost City 20
B5 Horror on the Hill 20
C1 The Hidden Shrine of Tamoachan 20
C2 The Ghost Tower of Inverness 20
D1-D3 Drow 20
EX1-EX2 Dungeonland/Magic Mirror 21
G1-G3 Against the Giants 20
I1 Dweller of the Forbidden City 21
I2 Tomb of the Lizard King 20
I3-I5 Desert of Desolation 21
I6 Ravenloft 21
L1 The Secret of Bone Hill 20
L2 The Assassin's Knot 20 N1 Against the Cult of the Reptile God 11 Q1 Queen of the Demonweb Pits 21
S1 Tomb of Horrors 20
S2 White Plume Mountain 20
S3 Expedition to the Barrier Peaks 17
S4 The Lost Caverns of Tsojcanth 20
T1 Village of Hommlet 20
U1-U3 Saltmarsh Series 20
UK1 Beyond the Crystal Cave 20
UK2 Sentinel 18 -
WG4 Forgotten Temple of Tharizdun 20
X1 Isle of Dread 20
X2 Castle Amber 20
X3 Curse of Xantathos 20
X4-X5 Desert Nomads Series 20
A1-A4 Scourge of the Slave Lords 20
B1 In Search of the Unknown 20
B2 The Keep on the Borderlands 20
B3 Palace of the Silver Princess 17
B4 The Lost City 20
B5 Horror on the Hill 20
C1 The Hidden Shrine of Tamoachan 20
C2 The Ghost Tower of Inverness 20
D1-D3 Drow 20
EX1-EX2 Dungeonland/Magic Mirror 21
G1-G3 Against the Giants 20
I1 Dweller of the Forbidden City 21
I2 Tomb of the Lizard King 20
I3-I5 Desert of Desolation 21
I6 Ravenloft 21
L1 The Secret of Bone Hill 20
L2 The Assassin's Knot 20 N1 Against the Cult of the Reptile God 12
Q1 Queen of the Demonweb Pits 21 S1 Tomb of Horrors 18
S2 White Plume Mountain 20
S3 Expedition to the Barrier Peaks 17
S4 The Lost Caverns of Tsojcanth 20
T1 Village of Hommlet 20
U1-U3 Saltmarsh Series 20
UK1 Beyond the Crystal Cave 20
UK2 Sentinel 18 -
WG4 Forgotten Temple of Tharizdun 20
X1 Isle of Dread 20
X2 Castle Amber 20
X3 Curse of Xantathos 20
X4-X5 Desert Nomads Series 20
N1 is a really fun module. The rest of you are clearly wrong. N1 gets routinely chosen as a good low-level adventure and I've had fun running it both times.
Though if you went to 1986 and could include B10 that would get my vote for best.
A1-A4 Scourge of the Slave Lords 20
B1 In Search of the Unknown 20
B2 The Keep on the Borderlands 20
B3 Palace of the Silver Princess 17
B4 The Lost City 20
B5 Horror on the Hill 20
C1 The Hidden Shrine of Tamoachan 20
C2 The Ghost Tower of Inverness 20
D1-D3 Drow 20
EX1-EX2 Dungeonland/Magic Mirror 21
G1-G3 Against the Giants 20
I1 Dweller of the Forbidden City 21
I2 Tomb of the Lizard King 20
I3-I5 Desert of Desolation 21 I6 Ravenloft 21 -3 = 18. AFAIC this isn't D&D. Obviously, a lot of people disagree. L1 The Secret of Bone Hill 20
L2 The Assassin's Knot 20
N1 Against the Cult of the Reptile God 12
Q1 Queen of the Demonweb Pits 21
S1 Tomb of Horrors 18 (This should be 17. -3 for a downvote.) S2 White Plume Mountain 20
S3 Expedition to the Barrier Peaks 17
S4 The Lost Caverns of Tsojcanth 20 T1 Village of Hommlet 20 +1. My go-to 1st level module.
U1-U3 Saltmarsh Series 20
UK1 Beyond the Crystal Cave 20
UK2 Sentinel 18 -
WG4 Forgotten Temple of Tharizdun 20
X1 Isle of Dread 20
X2 Castle Amber 20
X3 Curse of Xantathos 20
X4-X5 Desert Nomads Series 20
A1-A4 Scourge of the Slave Lords 20
B1 In Search of the Unknown 20
B2 The Keep on the Borderlands 20
B3 Palace of the Silver Princess 17
B4 The Lost City 20
B5 Horror on the Hill 20
C1 The Hidden Shrine of Tamoachan 20
C2 The Ghost Tower of Inverness 20
D1-D3 Drow 20
EX1-EX2 Dungeonland/Magic Mirror 21
G1-G3 Against the Giants 20
I1 Dweller of the Forbidden City 21
I2 Tomb of the Lizard King 20
I3-I5 Desert of Desolation 21
I6 Ravenloft 18.
L1 The Secret of Bone Hill 20
L2 The Assassin's Knot 20 N1 Against the Cult of the Reptile God 9 -3 Bandwagon
Q1 Queen of the Demonweb Pits 21
S1 Tomb of Horrors 17 S2 White Plume Mountain 21 +1, Interesting all the way through (oops corrected per below)
S3 Expedition to the Barrier Peaks 17
S4 The Lost Caverns of Tsojcanth 20
T1 Village of Hommlet 20.
U1-U3 Saltmarsh Series 20
UK1 Beyond the Crystal Cave 20
UK2 Sentinel 18 -
WG4 Forgotten Temple of Tharizdun 20
X1 Isle of Dread 20
X2 Castle Amber 20
X3 Curse of Xantathos 20
X4-X5 Desert Nomads Series 20