My vote was for Populous. Elite is one of the few all time greats, but to me it is in a different category as it wasn't original - simply a conversion to the Amiga. Others that I could easily have picked would have been It Came From The Desert, Silkworm, Rainbow Islands, Indy, North & South, Sim City, Maniac Mansion, Future Wars, Xenon II etc. Damn it's tough!
And even Stunt Car Racer. Such a great idea for a game. I'd love to see a modern version of this!