Alien because of HR Giger's iconic art style, among other things. Also Frank Herbert's Dune, the first planned film adaptation of which Giger also worked on (sometimes considered as the best movie that was never made). In addition to the cultural influence that the book series already had, Dune also more or less spawned the real-time strategy computer game genre (with Westwood Studios' Dune II).
But Jodorowsky's unfinished Dune project still had a significant influence on several major science fiction films and media, despite never being completed:
Alien (1979)
Dan O'Bannon, who worked on Jodorowsky's Dune, later wrote the Alien script
H.R. Giger's designs for Dune inspired his work on the Xenomorph
The Alien Xenomorph's design has roots in Giger's Harkonnen Castle concept for Dune
Star Wars (1977)
George Lucas was reportedly influenced by the Dune storyboards and designs
Jabba the Hutt's appearance may have been inspired by Baron Harkonnen's design
Blade Runner (1982)
Ridley Scott hired Dan O'Bannon and Moebius, who had worked on Jodorowsky's Dune, to help create the futuristic world
Contact (1997)
The opening space sequence was allegedly inspired by Jodorowsky's planned opening for Dune
The Incal (1980s graphic novel series)
Jodorowsky and artist Moebius recycled many concepts from their Dune work into this influential comic series
Check out the documentary "Jodorowsky's Dune" (2013). It explores how the pre-production work and assembled team for this unrealized film went on to influence much of modern science fiction cinema. It's worth a watch.