This is not an opinion, but a fact: "The Man Who Lost the Sea" is strongly in the running for the best science fiction short story of the twentieth century.
Others:
Thunder and Roses
The Golden Helix
Mr. Costello, Hero
Bianca’s Hands
The Skills of Xanadu
Killdozer!
Bright Segment
The Sex Opposite
[The Widget], [The Wadget], and Boff
It
A Way of Thinking
Slow Sculpture
Microcosmic God
A Saucer of Loneliness
… and my fear is great …
The Ultimate Egoist
The World Well Lost
And Now the News …
Affair with a Green Monkey
The Other Celia
Hurricane Trio
Maturity
That Low
Bulkhead
Derm Fool
The Touch of Your Hand
Talent
The Hurkle Is a Happy Beast
Why Dolphins Don’t Bite
The Professor’s Teddy Bear
Vengeance Is
The Graveyard Reader
The Pod in the Barrier
When You’re Smiling
The Silken-Swift
Occam’s Scalpel