Sci fi used to be vehicles, robots, guns/weapons and other props but now it seems a lot of sci fi is internal/hidden. Kind of like how horror used to be real monsters and now the scariest stuff are the things you can't see and you don't know who the enemy is (serial killers, crazy neighbors, terrorists, big conspiracies).
When I think classic sci fi I think flying saucers, rockets, War of the Worlds ships, air locks, helmets with antennas, tentacles, computer consoles with big buttons and lights, chrome (not the browser), robbie the robot, landing pods with spindly arms, jet packs.
I know most of those are not iconic images themselves but maybe it might spark an idea?