Don't know if this has already been recommended but, Isaac Asimov's Foundation series is a good one. Also Hitchhiker's Guide series.
I was turning this question over in my head (again) and remembered that the early Shadowrun novels were really good.
I've not read it, but Kim Stanley Robinson's Mars trilogy is quite well-respected. So is The Forever War by Joe Haldeman. There is also the Uplift series by David Brin, and the Culture series by Iain Banks.
Definitely. The Pip and Flinx books are terrific, and if you enjoy a bit of creepy-scary stuff, I recommend Midworld and Mid-Flinx. At least they scared the crap out of me; I've never looked at flowers the same way since... Some of the Heinlein juveniles are pretty good. Yes, science does figure into some of them, but it's not the technobabble crap. Heinlein's science was either based on already-known principles or at least plausible extrapolations of known principles. One of my favorites is Citizen of the Galaxy. And while Farmer in the Sky is technically obsolete (based on what we now know about Jupiter and its moons), it's still a good story.
Yeah, Mars is really great. It remains one of my favourite depictions of Mars in literature. The sequels are so-so, but the first one is really worth reading. Speaking of Ben Bova, another favourite story of his is an old novel of his called The Dueling Machine, available now on Gutenberg Press. It uses a similar concept to the holodeck before the holodeck even existed. There was one book I picked up at a random book story several years ago. It sounded interesting, so I picked it up, and I'm glad I did, because it was one of the funnest sci-fi reads I'd read in a long time. It was a gem. Up there with Douglas Adams. It's called The Last House in the Galaxy by Andy Secombe. The High Crusade by Poul Anderson is another fun read. Basically it asks the question of what would have happened if aliens had landed during the crusades, so it's part sci-fi, part speculative fiction.
Which was nothing new even then. Arthur C. Clarke did that in The City and the Stars back in 1956. What do you mean? Science fiction is a subset of speculative fiction. Did you mean part historical fiction? (A lot of Anderson's SF and fantasy fit that bill. His Time Patrol series was largely an excuse to explore the various historical periods and cultures he was interested in.)
Mars Trilogy by Kim Stanley Robison The Forever War by Joe Haldeman Hyperion Cantos by Dan Simmons Retribution Falls by Chris Wooding
Yeah, I guess I just really liked how it was done. A great little story. Yeah, that's more or less what I meant. I was having trouble trying to pigeonhole it I actually originally went with historical fiction and erased it and put speculative instead, thinking it would describe it best. I was thinking of speculative in terms of what ifs. I also thought of using alternate history, which likely would have been more accurate. My bad. I guess I should have stuck with my first description. I committed a redundancy. Still, it's quite a unique combination.