It might take while for me to go through them all but here are my favs at the moment:
Adam160591:
Adams Lemmings: naS gnimmeL awnabnoK
Adams 2nd pack: O....blivion
Sega! Levels: Adam's Sega Five Harder
Steaver370:
Challenges - Fewer Builders: Tetra Oblivion
Lemming racers: Impossiblemm Track
Lemming racers 2: 007: Moonracer
Lemmings Plus - Funny: Speed's the name, Lemmings's the game
Lemmings Plus - Strange: The "T" Level
Lemmings Plus - Weird: Poles of E-lemm-ination
Lemmings Plus - Wacky: The Lemming Gun
Lemmings Plus - Insane: Return of the T
Lemmings Plus 2 - Light: wINdiN' Up yOur lEMmiNGs
Lemmings Plus 2 - Neutral: Connection Error
Lemmings Plus 2 - Dark: Quick Clicks (Probably just for the name)
Lemmings Plus 2 - Evil: Quick Clicks II (Again, probably just for the name)
Ultimate Challenge: The Big 9
Ultimate Challenge 2: Just a minute and thirty seconds
Ultimate Challenge 3: Oblivion
Ultimate Challenge 4: A miner problem
Ultimate Challenge 5: This level is mine
Ultimate Challenge 6: All your lemmings are belong to us
Ultimate Challenge 7: Bull Ship
Wow, Steaver370 has a lot of levels.
Conway:
Conways lemedit remake: The Great wall of lemmingland
Sonic Green Hill zone - Introduction: Postcard from the Green Hill zone
Essman:
Fun: Training for tricky
Tricky: Armitage Shanks
Taxing: Just another annoying level
Mayhem: Prison escape plan
Ice Eagle:
Set 1: "Get to the Portkey!" and "Wacky Walls"
Set 2: 1001 ways to get out
Insane Steve:
Difficult: " Phone call from Europe" and "Up the pipe"
Menacing: The razors edge
Chaotic: Round Trip
Hopeless: The Mon0lith
Isu: (I have favourites in my own sets too!)
Isulemms: Cry for me (Rather Obviously)
Isulemms 2: "10 is a magic number" and "We are now at SEGA one"
Lemmings Classic Demo: The seven bridges of lemmingland
Style Trial (Part I): Every lemming in on it's own (Remake of SNES SUNSOFT 3)
Style Trial (Part II): The Angle Angel (Angles > Cries
)
Style Trial (Part III): Linear Patternz
Lemmings Classic: Space Lemmings!
Juanjo:
War: The Best Strategy
Old Temple: Expecting more from the rocks (Love this one)
Machine: Aim!!!!!!!!!
Skulls and Visceras: live after death
Galaxy: Galaxy Structure
Fantasy: Geometric "0"
Ahribar:
Michaels hard levels: It's all about survival
Michaels Notebook: Manclimber United
Dragonslover:
Red Dragons: Dragons Paradise
Shvegait:
Shvegait Lemedit remakes: Just Dig?
Special_Gunpowder:
Why Bother: "Lem'll fix it" and "The Laserium"
Drumnbach:
The real Mr. Lemming: Well I never
Others:
Crazy: Oh No! More Lemmings
The Land of Oz: Little Galactoids
Now, THAT took a while