- George R.R. Martin is one of the most popular authors working, and he straddles both genres. If you have any interest in historical fiction or epics, try A Game of Thrones (bonus: HBO series based on this volume starts in spring). For SF, his collections of short stories are better than the novels; Tuf Voyaging gives a good sense of the flavor.
- China Mieville: A prominent author who occasionally draws notice by the conventional literary establishment. His two best books are The City and the City (which is an odd genre-straddler) and The Scar. Prose is not his strongest suit, but for a sense of the New Weird subgenre, there's none better.
- Orson Scott Card: Ender's Game ONLY. Do not pass go, do not collect $200. Useful for analyzing the inner child of many libertarians.
- Connie Willis: If you like your lit fic to put you through an emotional wringer, this is the author for you. Several of Willis's more prominent works revolve around time travel, but she uses this device in the way that (IMO) speculative fiction is intended to be used: as a mechanism for examining the human condition. If you read one, make it Doomsday Book.
- Vernor Vinge: A Fire Upon the Deep and A Deepness in the Sky are awesome, in the sense of inspiring a sense of awe for the universe. It's
- Iain M. Banks: Also writes lit fic as "Iain Banks," so there's a natural progression. The Player of Games is probably the best entry point to his SF work, which chiefly deals with a post-scarcity society populated with humanoids and AIs.
I think Jack Vance is boring as all hell, but he gets accolades for his prose. Likewise, Bujold is often recommended but her stuff can be fluffy and mostly consists of an interminable series about a very short space captain. I have a love/hate relationship with Gene Wolfe's style, which can be opaque and muddled* at times, but if you do wish to try him, The Book of the New Sun is the place to start. Wolfe is meant to be read closely and rewards revisitation.
To avoid, at least for now and possibly forever:
- Neal Stephenson: These are not gateway books; the info dumps are too large, and Stephenson cannot write endings to save his life. Once you're a genre fan, go back and start with either Cryptonomicon or The Diamond Age.
- Ursula LeGuin: Much of her work has aged poorly. The Left Hand of Darkness is the closest thing to a gateway book I could recommend, and I'd really only do so if the reader had a preexisting interest in gender politics.
- Robert Heinlein: If you're not a teenage boy, a lot of his work is silly or distasteful.
- Frank Herbert: Like Heinlein, a titan in the genre, but best recognized for his overall contribution to mythos creation, not for prose or characterization.
- John Crowley: Unless you do a lot of drugs, avoid.
- Mervyn Peake: Gormenghast is ghastly. If someone tries to tell you it's like Tolkien but more literary, first punch that person in the mouth, then run.
Other authors that are NOT what you want: Donaldson, Brin, Octavia Butler, Sheri Tepper, Zelazny, Ann McCaffrey, Walter Miller, Kim Stanley Robinson, William Gibson, Sam Delany, Tad Williams. Some of these folks are fine authors, but they are best appreciated after a period of genre immersion. (Others are horrible, terrible, no-good-very-bad authors. I will not say which is which.)
* Sidebar: Is there a term for when someone takes the unreliable narrator one step further and the author himself becomes deceptive and unreliable? The predominant sensation I have when reading Wolfe is of being shown something through a deliberate haze.