As a child, The Martian, Pelucidar, and Tarzan books by Edgar Rice Burroughs
Out of the Silent Planet - CS Lewis
Just about anything by Heinlein...
Das Kapital by Karl Marx, what little I read of it in a Marxist economics class. I kept fallign asleep, so I read what other people wrote about it, and then parrotted back what the professor said in class... I got a B+
On the Beach - Nevile Schute (sp?)
Catch 22 - Joseph Heller
This Perfect Day - Ira Levin
A Canticle for Leibowitz - Walter Miller
Hitchhikers Guide - Douglas Adams
Animal Farm, 1984 - George Orwell
I never cared all that much for Vonnegut, but Harrison Bergeron was an eye-opener, especially the televised version with Sean Astin, which went farther that Vonnegut did in the story. Excellent teleplay, and a good story.
Harlan Ellison - Mostly for his "Dangerous Visions" collections, which introduced me to many other wonderful writers, like Fritz Leiber, Theodore Sturgeon and Piers Anthony. While I disagree with him on most political issues, I enjoyed his "Glass Teat" collections as well, and many of his short stories and novellas.
And the ever popular, "Too many to list!"
Mark