Outside of the Future History lies a large number of shorter works by Heinlein, which are nearly all from the 1940s and 1950s, before he made his primary focus the writing of novels. I will only cover a few of them that I consider to be particularly good, so you can consider these as recommendations.

• Magic, Inc. (1940) – This novella is a charming fantasy about a world where magic is simply normal and taken for granted. But there is company called Magic, Inc. that is trying to corner the market with a protection racket, and they are doing very well. It turns out the being behind this is actually a demon from the underworld. A couple of businessmen who are trying to hold out against this protection racket find a white witch to help them, and they travel to the underworld to find and confront the demon responsible, and the witch proves to be more powerful than the demon. You will most likely find this in book form combined with Waldo. This novella was nominated for a retro Hugo.
• They (1941) – This short fantasy story combines paranoia with solipsism. It is about a man confined to mental hospital because he is delusional. But you may have heard the saying that you aren’t paranoid if they are really out to get you. This is similar in some respect to The Truman Show.
• And He Built A Crooked House (1941) – What happens when you combine architecture with extra-dimensional topology? Well, maybe it is what happens in this story. An architect has an idea to create a house modeled on an unfolded tesseract, a four dimensional cube. If two dimensions gives you a square, and three dimensions gives you a cube, then four dimensions give you a tesseract. And they do build it, but they built it in California, so of course an earthquake comes along, and causes the house to collapse into the fourth dimension, with interesting results.
• By His Bootstraps (1941) – This is one of two Heinlein stories to explore the paradoxes of time travel. A fellow named Bob is writing a dissertation in the field of metaphysics to explain how time travel is simply impossible, when he is interrupted by a time traveler who tells him not to bother, it is all rubbish anyway. If you understand the bootstrap paradox you already know where this is going: the time traveler, and other people Bob interact with, are all Bob. But it is very well done.
• The Unpleasant Profession of Jonathan Hoag (1942) – This novella is a fantasy as well as a horror story. A husband and wife team of detectives is consulted by a man named Jonathan Hoag who says he has no idea what he does during the day. He has found a reddish-brown substance under his nails which could be blood, but he doesn’t know. They try following him, but experience some problems. In one case he turns on them nastily, in another they trace him to the thirteenth floor of a building that doesn’t have a thirteenth floor. Then other beings called The Sons of the Bird get involved. In the end it turns out that Jonathan Hoag’s profession is art critic, and the art he is judging is Earth. It was created by a promising student, but is it worthy of keeping? This novella was nominated for a retro Hugo.
• Waldo (1942) – This novella concerns a man called Waldo Farthingwaite-Jones, who was born with myasthenia gravis and as a result is congenital weakling who could not even hold his head up to drink or hold a spoon to feed himself. But it seems to have focused his intellect while also giving him a repellent personality. He is arrogant and considers himself superior. But in part due to his condition he invents what come to be known as “waldos”, devices which can multiply his strength, or conversely give him minute control. He put his hands into a device, and whatever action he does is duplicated on a larger or smaller scale in another device. These devices exist now, and are called waldos as result of this story, even by NASA. So this is the second time Heinlein gave a new word to the English language (the other being “grok”).
  
  He is brilliant, and as a result is consulted when major technical problem with power receptors that are failing. And at this point what had been a straightforward science fiction story becomes a fantasy. The solution lies in another adjacent dimension. Apparently you can pull power from this dimension all you want, and not just for the power receptors that power automobiles, but also for people. Waldo eventually heals himself this way and becomes a famous ballet dancer. This novella is usually found in book form paired with Magic, Inc. This novella won a retro Hugo.
• Goldfish Bowl (1942) – Two massive pillars of water mysteriously appear in the Pacific Ocean. Is this a natural phenomenon or the work of aliens? It looks like one sucks water up into a cloud which no one can enter, and the other seems to return the water. Scientists investigate, and it turns out to be aliens. The Earth is essentially their goldfish bowl.
• Jerry Was A Man (1947) – This is a very interesting story about a genetically modified chimpanzee that has had his intelligence increased so that he can be put to work in agriculture, and he has to go to court to claim rights. His lawyer presents evidence that he shares the essential traits of humans and wins the case.
• Gulf (1949) – This starts off as a James Bond type of story about an agent who we don’t know anything about. It is a good example of being dropped into the middle of a story, since he is being tracked by other forces we know nothing about. They eventually capture him, and he is confined with “Kettle Belly” Baldwin. This is the same Baldwin we see later on in the novel Friday, and he runs an organization of people who are of superior intelligence and devoted to protecting humanity. This is of course the same organization that Friday was a part of before Baldwin’s death put an end to it. The agent he rescued ends up joining the organization, there he receives advanced training. Here Heinlein brings in two of his enthusiasms. The first is the General Semantics of Alfred Korzybski, concerning which we may say more when we get to A.E. van Vogt. The other is the work of Samuel Renshaw, which also featured in Citizen of the Galaxy. The point of these two ideas is that people can be trained to think more rapidly and accurately. And the title in part refers to the gulf between people who have been so trained and ordinary untrained people.
• The Year Of The Jackpot (1952) – A statistician who works for insurance companies has a hobby of tracking cycles, and has noted that when a certain number of cycles peak together it can mean serious consequences for society. As an example, he saw that three of the cycles he tracks all peaked in 1929 when the stock market crashed. And now he is seeing a bunch of cycles lining up. And he notes odd behavior in society, like people suddenly taking off all of their clothes in public places for no reason. What can it all mean?
• The Man Who Traveled In Elephants (1957) – This is in my mind a very charming example of magic realism, which of course places it in the fantasy category. A salesman and his wife traveled the country looking for locations to sell elephants, accompanied by imaginary elephants. Now he is a widower, and still traveling. The attraction here is not the plot, but the atmosphere. This was one of Heinlein’s favorites of the stories he wrote.
• “—All You Zombies—” (1959) – This is Heinlein’s other classic time travel story. A man who was intersex goes back in time, and impregnates his younger female self, and she duly delivers a baby before getting sex assignment surgery to become the man who impregnated her. But the baby she delivers also turns out to be the same person, so in effect we have a person who is his/her own mother and father. This is the kind of thing that could conceivably happen if time travel is possible, which is why most physicists think it has to be impossible.

There are other Heinlein short works that a completist would want to look up, but I don’t consider them to be particularly significant And with that I am wrapping up the discussion of Heinlein, the last, but not least, of the Big Three of the Golden Age. He was given the unofficial title of the Dean of Science Fiction, which certainly testifies to the esteem he was held in by the science fiction community. But next I want to look at the origin of Space Opera, in the person of E. E. “Doc” Smith.