Ok, I WANT to suggest some Butler, but to be honest SO few of her stories stand on their own. Also, she not the most popular here.

None-the-less:

Wild Seed
Survivor
Clay's Ark

Now from Vonnegut:

The Sirens of Titan - I love, love LOVE this book!

Now from Steven King:

The Stand
Insomnia

Lastly, Asimov, Asimov, Asimov

If you're looking for a specific book, obiously, there's I, Robot. However, ANYTHING you pick up from him, will be great.

Good luck!

*edit*

Oh, oh, oh,

For something more contemporary:

Victor LaValle's Big Machine - Janey gave me this rec and it was pretty damned good.