I have to vote Dragon's Lair since it has been ported to about everything, still looks good and made a game mechanic popular that has infiltrated many game genres. Dragon's Lair truly is timeless.
Spy hunter, Track and Field (broke my joystick) Load runner and Manic Miner (which I played as Jet Set Willy 2) were amazing. Yet Dragon's lair was out of this world when it came out, mesmerizing. It ran on Laserdisc so not surprising it couldn't be ported to home consoles at the time.