Lemony Snicket for sure. He was one of the first authors who I started reading before I actually cared about literature. A lot of "vogue authors" lose steam after their first series. His 2nd series, All the Wrong Questions, actually improved the lore of Unfortunate Events.
Gregory Maguire. Although most people I've spoken to prefer the musical to the books, reading Wicked instantly improved my writing and was among the first books to encourage me to become a writer.
Agatha Christie has held my attention ever since I discovered her in 2010. I'm sorry to say I didn't correctly solve And Then There Were None, but I have correctly guessed the culprits of several novels afterword, most satisfactorily that of Hercule Poirot's Christmas.
I also think Toni Morrison is hilarious and witty. She writes mostly about the poor black community of the 20th century. One of the things I look for when I read is are catchy sentences; I first read "Recitatif" in 2011 as part of an American Lit class. It deliberately keeps the ethnicities of its characters vague in order to challenge racial stereotypes (you really can't even tell if the characters are black or white; you only assume so because of the social context).
Neil Gaiman has been a longtime favorite of mine. His story "How to Talk to Girls at Parties" had a big impact on my literary tastes. I saw Coraline for my 19th birthday, and I just had to read the book. I generally prefer his short stories to his books.
Aimee Bender is someone I've started reading recently. She writes very surreal magical realism stories. Her book The Particular Sadness of Lemon Cake is about an 8-year-old girl who can taste people's emotions through the food they cook.
Saki is another long-time favorite of mine. He uses the "Trickster" archetype for almost all of his short stories, and he was one of the earliest writers of Black Comedy.