I quite enjoyed Robert J. Sawyer’s Neanderthal Parallax, an anthropological SF trilogy about contact between our world and a parallel Earth wherein Homo sapiens neanderthalensis were the sole sentient species.
Susan R. Matthews. Give her Jurisdiction Universe a try starting with ‘An Exchange of Hostages’ if you can get a copy. Should be able to get it from amazon.com. Also possibly E.E. Knight’s Vampire Earth series. Start with ‘Way of the Wolf’ or jump in with the latest ‘Valentine’s Rising’. You don’t have to read them in order for them to make sense. And how about Philip K. Dick for something a little different?
The Hyperion Cantos series, by Dan Simmons. Starts with Hyperion.
The Night’s Dawn series, by Peter F. Hamilton. Starts with The Reality Dysfunction, Part 1: Emergence.
I have always enjoyed the Retief series of books by Keith Laumer. Those are played up for humor, of course. Bill the Galactic Hero by Harry Harrison is kind of a sendup of Starship Troopers.
At the recommendation of some of the locals, I have started reading the Honor Harrington series by David Weber, and they’ve been fun reads.
If you like “hard” science fiction, try the aforementioned Heinlein. You can’t go wrong with the classics, and Heinlein is probably the most easily available of those. Also go for the other two of the big three, asimov and Clarke. Larry Niven’s books are easily available, and the series started by him, “The Man Kzin-Wars” has good hard SF by a variety of writers.
Hal Clement and Robert Forward are great hard SF writers, too, but their works are getting harder to find with each year. This was true even when they were alive, but their deaths (very recently) just makes it worse.
Based on your favorites, I’d also recommend Vernor Vinge. And Robert Charles Wilson - an underappreciated author who has a gift for setting realistic characters in extraordinary circumstances. His most recent novel, Spin, is a good introduction to his work.
You know, I enjoyed the first book greatly, but the second was a step down and the third made me embarassed to be alive.
Check out China Mieville: Perdido Street Station, The Scar & Iron Council – they are set in the same world but not sequels. They are kind of gritty urban fantasy with steampunk elements.
You might also like some other British SF writers like Ken MacLeod & Iain M. Banks (all the Culture novels, but most especially IMHO, Player of Games.)
Jack McDevitt and John Varley are both great at the hard SF thing. Varley’s most recent ‘Mammoth’ hit me where I lived. And McDevitt’s ‘Priscilla Hutchins’ books make for really good multi-book character development.
Have you tried Steven Baxter’s Xeelee Sequence novels? Very hard (if highly speculative) science fiction with an emphasis on quantum mechanics and cosmology. Like many science ficiton authors, his ability to flesh out characters is somewhat limited, but he manages to apply hard physics principles to an engaging storyline and in service of the plot rather than the other way around. Vacuum Diagrams is a collection of short stories set in that universe and is a good introduction to both the concepts and major players (who are alluded to in his novels) and a good taste of the different styles in which he writes. He’s also written a couple of alt-histories (one, Voyage, explores a what-if Apollo Plus-type program), and an authorized sequel to Wells’ The Time Machine entitled The Time Ships, as well as a number of other novels.
I just started reading Greg Egan and wow! Just amazing ideas, and really intelligently written. I started with Diaspora and can’t wait to read his other stuff. I think a lot of his books are out of print, so you can get them cheap on amazon.
I’d second Heinlein’s The Moon is a Harsh Mistress.
Joe Haldeman’s The Forever War is simply a masterpiece. You should also read his Tool of the Trade, an outstanding Cold War what-if story.
My all-time favorite SF book, though, is George R.R. Martin’s Tuf Voyaging, a collection of interrelated short stories about a failed space trader who, through the greed and cutthroat mentality of others, ends up in sole possession of a ancient, massive and powerful starship. He sets out to earn a living with it, and has adventures ranging from the hilarious to the chilling. The book’s about absolute power, ecology, overpopulation, and the folly of war. I read it again every few years and find something new in it every time. Highly recommended.
I haven’t yet found anything that I’ve disliked by David Weber. His Honor Harrington series are great hard SF with character development spanning a whole lifetime. I also very much enjoy the Empire books; start with Mutineer’s Moon.
S.M. Stirling is also one of my current must-reads, but he tends more to the alternate history side than the hard space fiction. I can’t explain my love for him compared to my mild dislike of Harry Turtledove.