I’ve been on a cosmic horror kick lately, and what I’d really like to read is stories or novels of the awful and unfathomable on a spaceship. Stories where we go to them, poke what shouldn’t be poked, scan what shouldn’t be scanned, and things proceed from there.
Blindsight by Peter Watts (firewall series)
Hyperion by Dan Simmons
Revelation Space series by Alastair Reynolds
Alien by Alan Dean Foster
Haven’t seen it suggested yet, so I’ll throw out Linda Nagata’s Inverted Frontier series. Without giving away too much, explorers on the periphery of a collapsed posthuman civilization launch an expedition back towards its center, and along the way find various eldritch monstrosities – of human origin and otherwise – as they try to solve the mystery of the collapse. It’s more thriller than horror in tone, but it checks your other boxes quite well.
The Horus Heresy
Although I wouldn’t consider it an amazing book by any means I found “Infinite” and its sequel very unsettling.
Clark Ashton Smith has some cosmic horror stories fitting this description.