Cinefex Magazine ran a fall poll recently to identify the best VFX in cinema history. The final list:
1. Star Wars: A New Hope – Opening shot http://bit.ly/Hkc4aF
2. Jason & the Argonauts – Skeleton warrior battlehttp://bit.ly/1acUVvu
3. Blade Runner – Opening shothttp://bit.ly/1dt1viF
4. An American Werewolf in London: David’s transformationhttp://bit.ly/1dt1z26
5. The Abyss – Water pseudopodhttp://bit.ly/1acUYYg
6. 2001: A Space Odyssey – Star gate sequencehttp://bit.ly/HlN8i8
7. The Empire Strikes Back – Chase through asteroid fieldhttp://bit.ly/1ajfenp
8. John Carpenter’s The Thing – Chest defibrillation http://bit.ly/1bmtiww
9. Young Sherlock Holmes – Stained glass knighthttp://bit.ly/1iizXdN
10. Jurassic Park – T-Rex attack on children in vehicleshttp://bit.ly/1acVhCu
Personally, I think some of these things are on the list because they represented the cutting edge at the time rather than being particularly 'good'. The YSR stained glass knight and the pseudopod from The Abyss, for example, aren't particularly great, imo. But they were bleeding edge achievements of the day.
I think the chestburster scene in Alien was far more effective, both as a special effect and as a story device. I also think that something from T2 (either the T-1000 walking through the bars at the mental hospital or 'pouring' himself into the cockpit of the helicopter) would have been more deserving of inclusion.