Depends on what you're looking for @Alicia. Do you want something action packed or something more thoughtful? Big concepts with an emphasis on 'hard science' or something with more drama? Something with a military emphasis? Extreme Action - the 5 volume, main-sequence Polity works by Neal Asher featuring his saboteur-cum-tactician Ian Cormac. First book is Gridlinked. These need to be read in order. They feature a mix of science fiction tropes that were pretty much perfected (in their unique presentation) with Iain Banks' Culture novels, but Asher really excels in the action department and handles the tropes very well. Asher's society of the Polity is very much the opposite of Banks' Culture in mindset. - the 2 part Sucession duology by Scott Westerfeld: The Risen Empire and The Killing of Worlds. Very easy to read, a frenetic pace from the get go and in the classic space opera vein, albeit updated for more modern sensibilities. When it comes purely to fun-factor in space opera, this one is hard to beat. Both of these are more militarily inclined. Thoughtful - The Player of Games by Iain Banks, his second published Culture novel. The Culture books can be read in any order and this one is the most introductory friendly of the lot and gives you a good, mainstream impression of Culture society from within (most of the Culture novels offer fringe perspectives). Don't be deceived by the 'thoughtful' moniker - it is an intense story. - Neverness by David Zindell. Very much a planetary romance like Dune with space opera elements. Excellent world-building. Zindell can wax quite philosophical but his science fiction works are grand in scope and damn worthwhile. Neverness and its sequel trilogy is every much as epic in scope as Dune and its sequels. Both of these focus more on characters. Big Concepts - the Revelation Space trilogy by Alastair Reynolds starting with Revelation Space (or perhaps the collection Galactic North). Baroque, Gothic, dense and with an emphasis on science. It is required reading in contemporary science fiction. If you'd rather read a single novel, then pick up House of Suns, which is one of his best and unrelated to the Revelation Space books. - Marrow by Robert Reed. You can also start with his collection of short stories The Greatship as @kenubrion mentions. - A Fire Upon the Deep and A Deepness in the Sky by Vernor Vinge. Two independent instalments in a related setting. Both are excellent but Deepness, the second published, is my particular favourite and I think superior to the first. Many of Vinge's works deal with the concept of the singularity, though not with much emphasis in these two. In Vogue - The Expanse series by Daniel Abraham and Ty Franck, writing as James S. A. Corey. Through support and endorsement by the likes of George R. R. Martin and the fact that's it's being adapted for TV to be aired at the end of the year, this is currently one of the most popular 'space operas' that takes place within the solar system. I've read the first volume, Leviathan Wakes, and it was a fun romp. The Expanse also tries to get the science right. And since you mentioned temporal non-fiction works, you might want to check out Charles Stross' space opera Singularity Sky, which features a great take on time travel, though somewhat confusing to understand (for me) because of the physics. There's also some crazy magic-realism and slipstream aspects to the work. Overall, very interesting. The opening was fantastic. Essential are Iain M. Banks and Alastair Reynolds.