Probably Neuromancer by William Gibson for me.
Catskinner's Book of Lost Doors (the entire series), by Misha Burnett.
The Old Man's War series by John Scalzi
Most books by Robert A. Heinlein
I Will Fear No Evil is one I hand out pretty often.
It's got its moments to be sure, but I always thought that was one of Heinlein's weaker novels.
Toss up, either the first chapter of 2001 or in film The Thing or They Live.