I recently finally completed making my way through all of the Culture novels - thoroughly enjoyed every one, and was kind of sad to have reached the end!
Have you come across any other sci-fi authors that approach the style of Ian M. Banks? Otherwise, any recommendations for other sci-fi with the depth that the Culture series had?
Also check out Harry Potter and the Methods of Rationality for a rationistic fanfic crossover between scifi and fantasy if you haven't already.
You can probably use HN's search feature to find previous scifi reading recommendation threads for more.
"Iron Sunrise" and "Singularity Sky" come to mind. Maybe also "Quantum Thief".
What of the style / vibe / etc are you looking for more of?
If it helps, some fantasy authors I like are Joe Abercrombie, Terry Pratchett, Robin Hobb, Brandon Sanderson, Scott Lynch, Dave Duncan and Brent Weeks.
I like excellent character development, creative world-building and exciting stories that are plausible within those imagined worlds, wit that makes you laugh, good writing that has you marvel at the author's skill, and that special thing: immersive writing.
Beyond that, as a noob I don't know if there are sub-genres or particular styles of interest.
I had a quick gander at your suggestions, and the stories of Singularity Sky and Quantum Thief both sounds intriguing - I'll add these to my reading list, thanks :)
Dan Simmons (Hyperion saga, Olympus), Rameez Naam's "Nexus". Nick Harkaway's "Gnomon" is ridiculously good, and I basically buy anyone who wants one a copy of Cory Doctorow's "Walkway". Theodore Sturgeon is probably the closest SF I can think of to Pratchett, although he's Golden Era so suuuuper soft SF and doesn't have the humor. Bujold's "Vorkosigan" saga is one of the funnier SF books (while still being amazing and serious), and I hear good things about Scalzi's "Redshirts"
PS - Also checkout out what Hannu and Rameez get up to outside of writing, it's super cool.
You are the first person I've ever seen to mention that book. It is astonishingly and unreasonably excellent, and I recommend it every chance I get. I'm just beginning my first re-read now.