Picking just 10 is hard so think about it hard
1) Derelict/Engineer/Egg chamber discovery
2) Ripley facing the queen in her power loader shouting her unforgettable line
3) Ripley getting ready in the elevator to save Newt
4) Dallas' vent hunt
5) Ripley slowly venturing through the corridors in Alien during the climax with the cacophony of sounds and smoke
6) Ripley communicating with the Queen in the hive
7) Reveal of the true Ash
Kane's last meal...
9) Suicide grenade in the vents in Aliens
10) The Alien's slow otherworldly walk towards Lambert after killing Parker
So I only managed to pick scenes from the first 2 films...
Sorry if it has been done before.