Fiction
Philosophical (Free)
The Fable of the Dragon - Nick Bostrom (~19 pages)
A society forced to feed a dragon thousands of live humans each day. The only writing to make me cry.
Three Worlds Collide - Eliezer Yudkowsky
Deep in space, a human crew meet two new alien civilizations with deeply different values.
The Hero With A Thousand Chances - Eliezer Yudkowsky
A universe has been in peril for centuries, fighting a losing battle against The Dust. They summon a hero to unravel their riddle.
Free
Harry Potter and the Methods of Rationality - Eliezer Yudkowsky (~2600 pages)
A Harry Potter fanfic where (among other things) Harry is raised by a biochemist and tutored in scientific and rational thinking. He goes off to Hogwarts and much shenanigans ensue.
Paid
Mort - Terry Pratchett (~260 pages)
A comedy following Death's new apprentice, Mort, and his adventures across Discworld. My favorite paid written fiction.
And Then There Were None - Agatha Christie (~300 pages)
A mystery novel following featuring 10 strangers who are killed one-by-one on an island.