Stranger In A Strange Land is probably the best book he ever wrote, and quite possibly one of the best books ever written, period...especially if you have the unabridged edition. A couple of those titles are technically considered "Young Adult" reading, but still, nice collection. If I may, I also recommend I Will Fear No Evil, Friday, The Moon Is A Harsh Mistresss, The Puppet Masters (which "Invasion of the Body Snatchers" was based off of, and referenced in "The Faculty"), Methuselah's Children, Time Enough For Love and The Cat Who Walks Through Walls (both of which deal with Lazarus Long and should be read in that order) . A couple of those are also considered "Young Adult", like Methuselah's Children, but still great fucking reads. Who else do you like for sci-fi?