Well, Heinlein did write STARSHIP TROOPERS, which was made into a successful film with a sequel or two and a TV series based on it; he wrote the first major work about aliens taking over people's minds in the much imitated THE PUPPET MASTERS (1951); had a TV show on the air in 1950 based on his juvenile SPACE CADET. Kicked off the SF boom by co-writing DESTINATION MOON, based on his novel ROCKETSHIP GALILEO. He didn't care much for film work, but he was in demand. STRANGER IN A STRANGE LAND has a certain amount of fame attached to it, as well. He was the first SF writer published in the slicks. Take a look at the SF shelf in your local bookstore and you'll find he still has plenty of novels in print even though he's been dead for 22 years. I can only add that if you don't know Heinlein you don't know science fiction.

LeGuin certainly is among the most famous, as Ryan points out. I don't know how we could have neglected her up to now.