I just finished reading Heinlein's novel Stranger in a Strange Land. For someone who's read a bunch of science fiction, this was the first Heinlein novel that I've read, and I'm glad I picked it up. I never realized that the word "grok" came from this novel. The word is fairly prevalent in programmers lingo, and after reading the novel I grok what people mean by it a little better.
In these older SF stories, it's fun to see what technologies are mispredicted. In the novel, Heinlein has people riding flying cars, and appliances that cook for you. And yet video cameras still required "tape", and phones were firmly tethered to the wall.
Of course, as with a lot of good science fiction, it's the ideas, story, and the characters that make it a good read, and this one is pretty good. I already have a copy of Starship Troopers sitting on a shelf, I hope to tackle that next.