I slept way too long on Peter Watts and Ted Chiang. Both recent new faves

First, as this is my first post here: hi all!

Regarding the topic, in no particular order, they differ so much..

Arthur C. Clark "2001: A Space Odyssey" - a classic, the book with the best movie adaptation ever
Stanislaw Lem "The Invincible" - great book about life and evolution
Neal Stephenson "Snow Crash" - my favorite cyberpunk novel
Arkady and Boris Strugatsky "Roadside Picnic" - the best approach to the issues of extraterrestrial contact

The Locked Tomb series by Tamsyn Muir!!!!!!!!!!!!!!!!!!

Perdido Street Station by China Miéville. Any of the Bas Lag books, really. Incredible world-building completely pulls you in. You feel like you are there, that you know this world. Incredible stuff.

Vorkosigan Saga by Lois McMaster Bujold, with Barrayar as my absolute favourite book in the series. I love the mix of historical with scifi and the way it explores issues of reproduction and disability while having very fun, whacky hijinks.

Big question...

Kim Stanley Robinson - Mars Trilogy, Science in the Capital series, Antarctica
Neal Stephenson - Anathem, Snow Crash, The Diamond Age
Ken MacLeod - Fall Revolution series, Execution Channel
Robert Heinlein - Podkayne of Mars, Moon is a Harsh Mistress, Starship Troopers
Sean McMullen - Greatwinter series
Joe Haldeman - The Forever War
Connie Willis - Doomsday Book
Ursula K. LeGuin - The Dispossessed and The Left Hand of Darkness
William Gibson - Neuromancer, The Bridge Trilogy, and the Blue Ant books
Iain Banks - Consider Phlebas
Samuel Delany - Dhalgren
Maureen McHugh - China Mountain Zhang
Nicola Griffith - Ammonite
Pat Murphy - The City, Not Long After
Frank Herbert - Dune
Arthur C. Clarke - Childhood's End, Rendezvous with Rama
David Brin and Gregory Benford - Heart of the Comet
David Brin - Startide Rising
Walter M. Miller, Jr. - A Canticle for Leibowitz
N. K. Jemisin - The Fifth Season
Charles Stross - Halting State
C.J. Cherryh - Downbelow Station
Larry Niven - Ringworld, Protector
Larry Niven and Jerry Pournelle - The Mote in God's Eye

There are some books I'm not sure I fully consider science fiction and so hesitate to recommend in this context - like Connie Willis' "To Say Nothing of the Dog" (even "Doomsday" felt a bit of a stretch) or "Hitchhikers Guide to Galaxy" or China Mieville's "The City & The City." And there's a couple books that would have been on here, but their authors' views on some social and political matters make them impossible to recommend.

Some favourites of mine in no particular order:

The Peace War and Marooned in Realtime by Vernor Vinge (available together as "Across Realtime") and anything else by him tbh. They are about a technology that can freeze an area of space in time and the uses it is put to. In the first book it is used mostly as a weapon. In the second, the only remnants of humanity are a handful of people who were frozen in time and wake up to find the rest of humanity gone. They are from societies with different levels of technology, but the book is kind of a murder mystery as well.

The Expanse series by James S. A. Corey. I really like the portrayal of the colonisation of the solar system in this series, and how it splits humanity into different groups. When a technology from an extinct alien civilisation opens a portal to thousands of other solar systems it kicks off a series of conflicts, and the crew of an independent warship, made up of members of the different factions, are central to restoring peace.

Station Eleven by Emily St. John Mandel. It's about a post-apocalyptic world but with an emphasis on how people try to preserve culture, particularly a group of actors and musicians who travel around performing Shakespeare and classical music. It's a really interesting take. It's barely science-fiction I guess but I really liked it.

The Dispossessed by Ursula K. Le Guin. It's about a physicist from an anarchist moon who visits the planet of his origins, where capitalist and authoritarian communist sociopolitical systems dominate, in order to complete and share the theories he has been working on. It's a really interesting depiction of an anarchist society, and its benefits and flaws.

The Murderbot series by Martha Wells. Really fun series about a security cyborg who breaks its programming so that it can do whatever it wants. It mostly just wants to watch TV undisturbed, but ends up being dragged into various murdery adventures. Probably one of the most relatable and charming protagonists I've ever encountered.

Roadside Picnic by Boris & Arkady Strugatsky. This one's about an alien visitation that has left contaminated "zones" at several sites around the world where alien technologies are left scattered around. People called "stalkers" make a living retrieving technology from the zones but they and their loved ones end up mutilated as a result.

Stories of Your Life and Others by Ted Chiang - it's a short story collection but they are really good. The movie "Arrival" was based on one of them.

Love the Expanse (who doesn’t?), one I really liked is the Silo series. It’s not based in space so a bit different to the ones mentioned.

Some of my favourites:
Murderbot series by Martha Wells
Imperial Radch series (Ancillary Justice/Sword/Mercy) by Ann Leckie
Vorkosigan Saga by Lois McMaster Bujold
Dogs of War duology by Adrian Tchaikovsky
The Expanse series by James S A Corey
Monk & Robot series by Becky Chambers

I've not read the Xeelee series so can't say if there's any similarities, but they are all excellent sci-fi series and well worth your time.