I swear we already had one of these, although perhaps not with the "essentials" title.

House of Leaves
East of Eden
The Wind-Up Bird Chronicle

 

Oil!
Paradise Lost (I like epic poetry, and more people should too)
Siddhartha
The Metamorphoses

God forbid anyone recommend Twilight.

 

Lotta good ones mentioned already!
Off the top of my head, I'd add:

1984
Watership Down (El-ahrairah has the best gbatemp name, imo. i'm jealous of it....)
The Thief of Always
Dreamboy
The Road
As I Lay Dying
the Discworld series
Catcher in the Rye

 

-House of Leaves (it is unlike anything I have ever read before, and I loved it)
-Dune (great sci-fi book, dunno about anything beyond the first though)
-Hobbit + Lord of the Rings (kinda reminded myself I want to read it all over again, the writing really transports me there in my mind)

A few others, while probably not as prolific as the above,
-The Long Walk (totally F'ed up sci-fi story by Stephen King when he was calling himself Richard Bachman, would make a great movie)
-Sphere (an amazing Michael Crichton page-turner, read in 2 days)
-The Ruins (suspenseful horror story)

 

The Miracle of Right Thought
The Laws of Thinking
Rich Dad, Poor Dad

 

Eragon series, it's like lord of the rings but for our time =]

 

Harry Potter
Darren Shan