This is a difficult question that I’m likely to get wrong since it changes all the time. In no particular order other than that in which they occurred to me:

Joseph Conrad

English was his second language, yet this man wrote the smoothest prose you’re ever likely to read. Every sentence is a treasure. Sometimes, when reading Conrad, I lose track of the story because I’m reading a sentence over and over, just marveling at its ingenuity. Who cares about plots and characters when you can command the English language the way that Conrad does? With Conrad, it’s not so much about the story as it is about the way he puts it all together. Perhaps because English was a second language, he was able to master it better than most. In any event, he writes in English better than I do and it’s my native language.

Aleksandr Isayevich Solzhenitsyn

Solzhenitsyn is pretty much the opposite of Conrad in the sense that it’s not about the writing necessarily; it’s about the story. Like most people, the first book I read by him was One Day In The Life Of Ivan Denisovich. It started me on a lifelong passion for Russian fiction and non-fiction. Though very short, Ivan Denisovich is a perfect book. It superbly encapsulates Stalin-era Soviet labor camps. If you’re looking for non-fiction in the same vein, there are no better books on the subject than The Gulag Archipelago series.

Charles Bukowski

What can be said about Bukowski? Some say he is a one-trick pony, i.e. he only writes about wine, women and hard luck, and while he might write better than most on the subject, it’s still the same trick over and over. I disagree and it’s probably because I’ve read so much of his work. When he became a writer proper, he wrote every single day. It’s impossible to only write about three things if you write every day. There is no one on earth, with the exception of my dog, that I’d rather curl up with after a long, hard day. Nobody gets it like Bukowski, which is why he lives in my bedside table.

Joan Didion

This is a new addition to the list. I recently read her 1,000+ page non-fiction compilation, We Tell Ourselves Stories In Order To Live. What I like about her is her easy, conversation style of writing. When you read Didion, you feel like you know her, like you’re sitting down with an old friend and listening to her tell a story. She’s got such a natural way with words.

Douglas Adams

If you haven’t read The Hitchhiker’s Guide To The Galaxy, you should be embarrassed for being so very wrong. I don’t care what your excuse is, you are lacking. Go read it right now to become a better person. Every time I read Adams, I want to go exploring. I want to get in my car and just drive around aimlessly, exploring our little world since we don’t have interstellar space transportation yet and probably won’t in my lifetime. The Hitchiker’s Guide will make you very sad that we don’t. Adams is inventive, compelling and just plain funny.

Runners Up: Authors who are spectacularly awesome:

George Orwell
William Shakespeare
Raymond Chandler
Louis-Ferdinand Céline
Neal Stephenson
Warren Ellis
John Steinbeck
Edgar Allen Poe
Franz Kafka
Väinö Linna
Dr. Seuss

Runners Up: Books that are spectacularly awesome:

A Clockwork Orange by Anthony Burgess
Dead Souls by Nikolai Gogol
Hunger by Knut Hamsun
Seven Brothers by Aleksis Kivi
Woman In The Dunes by Kōbō Abe
Johannes Climacus by Søren Kierkegaard
Darkness At Noon by Arthur Koestler
Red Harvest by Dashiell Hammett
All The King’s Men by Robert Penn Warren
In Cold Blood by Truman Capote
The Gone Away World by Nick Harkaway
Winesburg, Ohio by Sherwood Anderson
World War Z by Max Brooks

And probably a thousand more that I’m forgetting because I never stop reading.