Python
Super Freak
I think the original Predator completely blew expectations out of the water. Kind of like the original Terminator, a 'B' grade movie that no one making it would ever imagine it becoming an icon in the film industry.
Both of these movies (Along with Alien) had three very important factors in common which probably secured that success. If not initially so much, but certainly in long term cult followings.
1: Fu**ing awesome creature design! As in the best in cinema history.
2: Directors that really knew what they were doing.
3: Amazing soundtracks and sound design.
Lose even one of those and those movies become instantly forgettable. If Stan Winston hadn't come onboard Predator last minute and saved the day, many of us probably wouldn't even be in this hobby now.... And we'd all be much wealthier.