The Last Question - Isaac Asimov

That was my first thought, but since you've posted it my runner up is "The Egg":

http://www.galactanet.com/oneoff/theegg_mod.html

They're made out of meat

http://www.terrybisson.com/page6/page6.html

The truth of fact, the truth of feeling by Ted Chiang https://subterraneanpress.com/magazine/fall_2013/the_truth_o...

This story changed the way I saw writing with the way it portrays it as a tool that can be used or misused just like any other.

I'm a huge fan of this format for sci-fi, so it's a hard choice. Probably "Goodnight Mr. James" by Clifford Simak.

Honorable mentions to:

"Microcosmic God" and "If all men were brothers would you let one marry your sister?" by Ted Sturgeon

"Bordered in Black" and "Neutron Star" by Larry Niven

"Blood Music" by Greg Bear

"Special Delivery" by George O. Smith

"The Gold at the Starbow's End" by Fredrick Pohl

"The Feeling of Power", by Isaac Asimov. In this story, humans have forgotten how to do basic math, except for one man, who regards it as a hobby.

edit: http://john.regehr.org/reading_list/power.html

Not my favorite, but an underrated one: The Machine Stops by E. M. Forster.

Forster is better known for writing period romances like A Room with a View. The Machine Stops, written in 1909, deals with issues of isolation and alienation that come with advances in communication technology, and it sort of kind of predicts the internet.

The Seventh Voyage from The Star Diaries by Stanislaw Lem http://english.lem.pl/works/novels/the-star-diaries/154-the-...

Fondly Fahrenheit by Alfred Bester: http://www.editoreric.com/greatlit/books/Fondly-Fahrenheit.h...

Three Worlds Collide - http://lesswrong.com/lw/y4/three_worlds_collide_08/

Just came across this nice reddit https://www.reddit.com/r/shortscifistories/

The Crystal Spheres[0] by David Brin

[0]https://en.wikipedia.org/wiki/The_Crystal_Spheres

'Understand' - Ted Chiang (technically a novelette)

March Hare Mission by Ford McCormack

'Flowers for Algernon'