I enjoyed Simon R Green's Deathstalker books, which are very, very space opera-y. I also liked (although I'm pretty sure I'm way in the minority here) Kevin Anderson's Saga of Seven Suns. For harder sf, I like Kim Stanley Robinson (although not all of his stuff is sf, all of it's good IMO) and Charles Stross.

One of the most unique science fiction books I've ever read was Eifelheim, by Michael Flynn. Unique in a good way, though.

Mass Effect is sometimes dropped into the "space opera" category and there's a series by author Catherine Asaro which begins with "Primary Inversion" which neatly falls into the same. The books are primarily character-driven, as each book focuses on a member of a particular family (the Valdorias), but the political backdrop is never far behind. The author herself is a quantum physicist and a ballerina - revealed in her heavily scientific descriptions of their weaponry, communication, and travel systems and the appearance of several characters who are dancers. The main tagline is "what would happen if humans achieved space travel and reached the stars only to find...they were already there?" - operating off the idea (that's very Stargate, though I admit I didn't make the connection over a decade ago when I first started reading these books) that a small group of humans were harvested and reseeded in another part of the galaxy by another species. They were left with advanced technology and these other humans reached their pinnacle very quickly, developing myriad technologies and reliance on a certain trait of telepathy/empathy only to collapse just as quickly. They recovered, but being reliant still on certain traits, lean heavily on one of the last family lines to carry these traits in full. There's also bits in there about genetic tomfoolery and what happens when you try to play god and there is a certain degree of romance (so if that isn't your cuppa, I would instead steer you away), but there are certain things, like the dice game Quis, which is built on physics and mathematics that I barely understand, which are incredibly fascinating. And at the end of the day, royalty, genetic anomaly, or military commander, they're still PEOPLE.

She's written several standalones which are quite good as well, including "Alpha" and "The Veiled Web".

I'd be remiss if I didn't recommend Frank Herbert's DUNE - I admit the series seems to be unending at points and I have not completed the entire series, but I've read the first three and enjoyed them a great deal.

Raymond Feist writes a strange fusion of fantasy and sci-fi, so he's one to check out too - I haven't read the series that's more sci-fi but the Conclave of Shadows trilogy is predominantly fantasy with a peek at the alien species which has a bigger role in one of his other series.

I know I've got others I can rec but without my bookshelf in front of me it's a bit more difficult than I'd like!

Octavia Butler’s Xenogenesis Trilogy! (Dawn, Adulthood Rights, & Imago)

It's a post apocalyptic setting when survivors wake to realize that aliens have saved what was left of the human species from extinction during a massive war. In return for this saving, the aliens expect the human to partake in genetic trade with them, and the books chronicle the re-population of Earth.

Look up some reviews/synopsis, because I'm terrible at summaries, but they are *really* good books!

Julie E. Czerneda. She's a biologist, so her alien species and interstellar civilizations are hugely varied, funny and creative. I'm still working through all her books myself, but try the Trade Pact Trilogy (starting with A Thousand Words For Stranger) and Web Shifters Trilogy (starting with Beholder's Eye). I'm a relative newcomer to scifi myself, and have found her books easy to digest.

For classics, William Gibson's Neuromancer has stood the test of time well for me, and Ursula K. LeGuin's The Left Hand of Darkness is just amazing.

Alien species
Mary Doria Russell - The Sparrow (also, the follow-up novel Children of God)
Connie Willis - Uncharted Territory

AI
Bruce Sterling - Neuromancer (he may have others on the subject, but this is the only one I've read)

Future Civilizations
David Marusek - Counting Heads (I think this is the first novel in the series)
Connie Willis - Fire Watch; To Say Nothing of the Dog; Doomsday Book; etc.
Jasper Fforde - Shades of Grey (his Thursday Next series is an alternate history- starts with The Eyre Affair)

You may want to also check out Cory Doctorow.

There are plenty of others out there - this is just a smattering. A lot of SF novels I find by just browsing the SF/F section in my local library and picking up novels that look interesting.

Whee, Mass Effect! :D

I'm going to recommend you two series here:

Lois McMaster Bujold's Vorkosigan series

Sharon Lee and Steve Miller's Liaden Universe

Both touch on future societies, and are probably my two favorite space opera sci-fi series of all times.

Oh, and for virtual reality, I'd be remiss in not recommending Ernest Cline's Ready Player One. Easily one of my favorite books from last year.

Edited at 2012-02-27 10:25 pm (UTC)

Left Hand of Darkness by Ursula K. LeGuin
Dune by Frank Herbert You probably don't want read the whole series, but the first one is pretty good.
The Science Fiction Hall of Fame Volume one is a collection of older short stories, Volume two, if you can find it, is
a collection of novellas from the same period.

Books I've never read, but have heard good things about:
Iain M. Banks' Culture Series
Snow Crash by Neil Stephenson
The Day of the Triffids by John Wyndham
The Hitchhiker's Guide to the Galaxy by Douglas Adams

A couple of good series about far-future human civilizations:

The Diving Universe by Kristine Kathryn Rusch:
Diving into the Wreck
City of Ruins
Boneyards

The Night's Dawn Trilogy by Peter F. Hamilton:
The Reality Dysfunction
The Neutronium Alchemist
The Naked God

John C. Wright's Golden Age, Phoenix Ascendent, and Golden Transcedence. So far future as to be quite alien. Count To Trillion, too, but that's still in progress.

Rick Cook's Limbo System. A first contact story.

Jack Campbell's Lost Fleet series. Dauntless, Fearless, Courageous, Valiant, Relentless, and Victorious Future civilization

Lois McMaster Bujold's Vorkosigan series. Future civilization

Only You Can Save Mankind by Terry Pratchett. Sort of. But it's definitely got aliens! And it's a great book

Archangel by Sharon Shinn. Future civilization

Endless Blue by Wen Spencer. Future civilization and aliens. A Brother's Price. Not future, not alternate history --that can be discerned -- but world-building with no fantasy elements.

Brothers of the Snake by Dan Abnett Future civilization. And aliens, too. Also The Founding , the omnibus of the first three of his Gaunt's Ghosts books in the same universe. Ciaphas Cain: Hero of the Imperium by Sandy Mitchell is another omnibus in the same universe. They're all good, even if you have to go to the media tie-in section for Warhammer 40,000 to read them.

Piers Anthony's Prostho Plus. Probably the only book of his I'd actually recommend. Mercycle is also sci-fi of a sorts, though it takes place on earth, but is much more juvenile and reminiscent of his Xanth stuff.

Some folks really enjoy the Man-Kzin Wars by Larry Niven. I wasn't that enthralled by them but some of my friends were. I think there are a dozen or so books in that series.

Most of the stuff I have enjoyed have been anthologies. There are a couple good ones out there. One is titled "Gateways" and is edited by Martin H. Greenberg.

Obviously I've already said I think Left Hand of Darkness by LeGuin is a must in an earlier comment.

For light fluff, Robert Asprin's Phule's Company can be amusing, but it's very human-centric. Frankly I'll tell you that the first two books are worth the read, the rest really aren't.

The Faded Sun Trilogy by C. J. Cherryh is an absolute must though for what you're asking for.

Hitchhikers and Dune will get a lot of play here, but I think they're definitely YMMV books, particularly Dune.

Robert A Heinlein: The Moon is a Harsh Mistress; Starship Trooper; A Stranger in a Strange Land; Citizen of the Galaxy; Space Cadet

Spider Robinson's books about Callahan's bar.

Fritz Leiber The Big Time

I've already seconded Butler, Bujold, and Rusch.

The Necessary Beggar (not in print) or Shelter (in print), by Susan Palwick - Palwick is an amazingly compassionate writer of character-centered stories involving family, love, justice, and conflict.

Archer's Goon, by Diana Wynne Jones - marketed as a kid's novel, but all her stuff is amazing. Most of her stuff is more fantasy, but this has tech.

Expendable, by James Alan Gardner - fast-paced novel about Festina Ramos, one of Earth's Explorer Corps. People with aesthetic defects (hers is a birthmark) are no longer allowed in society, so are pushed into the Explorer Corps, which is sent out to new planets to figure out whether humans can survive on them. You'd think this would be grim, but Festina is wry and funny - and eventually wins her freedom.

Stories of Your Life and Others, by Ted Chiang - Ted Chiang is the best short story writer ever. Seriously. No matter what field. No matter what he writes. No matter what anyone else writes. I don't know how he does it, he just produces perfect stories (most of which are sf).

Cyteen, by CJ Cherryh - Ariane Emory is a genius scientist-slash-dictator running her own little enclave in one city. When she's murdered, the only thing her subordinates can think of to do is to clone her and design all the minutia of Ari II's childhood so that her personality replicates Ari I's as much as possible. So Ari is this little genius kid whose rewards and punishments are based on someone else's childhood, while she is surrounded by the supporters and enemies of her predecessor, a middle-aged woman capable of both brilliance and rape. Tons of ethical questions, intrigue, and thought problems.

Hellspark, by Janet Kagan - best first contact/linguistics novel ever. Tocohl Susumo, a trader, is forced into impersonating a judge sent to determine whether an enigmatic species is sentient, which will govern the allocation of resource exploitation rights. Again both funny and dramatic (I like the mixture).

Do you want fantasy recs too?

Tons of great recommendations here. One recent release that covers the virtual reality aspect really well is Ready Player One by Ernest Cline.

Ummm....
"Ender's Game" by Orson Scott Card
"Do Anrdroids Dream of Electric Sheep" by Philip K Dick
On a Pale Horse" by Piers Anthony
"I Have No Mouth and I Must Scream" by Harlan Ellison
"Lucifer's Hammer" - Jerry Niven and Larry Pournelle
"A World Out Of Time" - Larry Niven
"Clans of the Alphane Moon" - Philip K Dick