Here are mine:
Absolutely adore Michael Marshall Smith. Spares and Only Forwards in particular
Some great picks there!
I really love Robert McCall, in-particular his 2001: A Space Odyssey work - I have some of it on my wall!
Alex Ichim does some incredible work, I’m a huge fan of spacecraft that have nods to current aircraft designs.
H. R. Gieger (Alien) of course - really just an astonishing style that produces such beauty in the horror, and I really like how he blurs the lines between organic and machine.
Jon McCoy does some incredible concept art for major projects, but I love his personal work the most.
I grew up on Warhammer 40,000 and just poured over all the amazing artwork in the books for many years - I particularly like John Blanche’s work as it has sort of a chaotic quality, such fine detail coupled with “noisy” abstraction. But really all of their artists, 2D and 3D, are amazing - so much iconic sci-fi imagery.
There’s more I’m sure but they’re not coming to mind!
EDIT: I really love the art deco sci-fi/space posters from the 1920’s and 1930’s, but I couldn’t name an artist. I really want to get a print for my wall as they look so cool!