Favorite Sci-Fi.. crumbs.. where to start , I have a few books & films in my collection.
When Worlds Collide (1951), long overdue for a sequel or even a series perhaps, the possibility of life on the rogue planet was never broached and the closing scene has pink pyramids in the background.
Silent Running 1968 - with the worries about global warming this movie is more relevant than it ever was back then, of course the real stars of the film were the drones Huey, Duey and Louie and that closing scene of the little robot with a watering can has been described as a real geek tearjerker.
DUNE - directors cut 1985, if Star Wars was classic 'Space Opera' then Dune has to be the equivalent of Shakespeare. It was a brave attempt to shoehorn an awful lot of plot and sub-plots into a movie that should of been an hour longer. This was redressed a few years ago by the Sci-Fi channel who did a mini-series that took the script more closely from the book. Rumor has it that they are going to be doing a remake of the original in the next few years. (along with a remake of Death Race 2000 , I do hope the get some of the original cast to do cameo appearances)