Robert Charles Wilson, already mentioned, is the best Canadian sf writer, BTW. Nalo Hopkinson, from Toronto, should be mentioned, along with Julie Czerneda and James Alan Gardner also from Ontario.
Some British writers that may be easier to obtain and/or better better in known than the U.S. include M. John Harrison, Geoff Ryman, Charles Stross, Iain Banks, Ian Stewart, Ian Watson,… heck just stock anyone named Ian. Cory Doctorow is American but living in England these days and he’s become well known because of his Boing Boing blog. I think Neil Gaiman is the reverse, now living in the U.S. but he sells even better.
Neil Stephenson started in sf and his latest work is on the Venn intersection of fantasy, sf, and mainstream, but is wonderful and sells like crazy.
All are good places to go for working writers. You should have some of the dead white men classics, of course, but support for today’s writers means there will be a future for the field, and future classics to stock.
Robin Hobb (best damn romance in a fantasy novel I’ve ever read; her ability to write characters that are real and riveting is absolutely amazing)
Trudi Canavan (I really liked the Black Magician trilogy)
George RR Martin (a must for fantasy readers; the man is pure genius at political fantasy)
Jim Butcher (unless he’s shelved in the mystery section; he writes hardboiled fantasy detective novels)
Miss Snark highly recommended The Bartimaeus Trilogy, but I haven’t personally read them. They’re on my wish list, though.
For starters, I endorse Polycarp’s list. There are a few authors on it that wouldn’t appear on my “must have” list, but none that I would suggest avoiding. I would suggest that Niven’s strongest work is in his short stories, so don’t neglect the collections in favor of novels.
For fantasy:
Mercedes Lackey–I would guess that you actually carry Lackey books, and just didn’t mention them. If you don’t, however, you should certainly consider it. She’s both prolific and popular, a good combination for a store. Her work tends to appeal to more women than men, I think, and may be a good way to lead female customers into fantasy.
P. C. Hodgell–She’s a personal favorite who doesn’t get nearly the attention or readership she deserves. She writes very dense, intricate fantasy. It tends to be dark, but with a great deal of situational humor and engaging characters. The downside is that she’s not very prolific; she has only a few novels out, all in one series, and a collection of short stories that are mostly about the protagonist of the novels. On a more promising note, the next book in her Kencyrath series is due out this summer, I believe.
P. N. Elrod–Her Vampire Files series is about a reporter-turned-vampire in Prohibition-era Chicago. It’s pretty extensive, and most of the books are fun, light reads–think gumshoe/gangster with a twist. Some of the later books are darker.
I am currently completely in love with Bujold’s fantasy Chalion books. I haven’t started the sf series yet, but the first one is next in my to-be-read pile.
Most of the ones I would be shouting about are already mentioned: Nix, the divine Robin McKinley, Hobb, Patricia McKillip.
So, here’s a couple I haven’t seen:
Greg Keyes’s The Kingdoms of Thorn and Bone. The Briar King is simply one of the best fantasy books I’ve ever read. The third book of four came out yesterday. Woo!
Chaz Brenchley’s Outremer books start with The Devil in the Dust, and are compelling. Beautiful writing throughout a 7-book series.
Pamela Dean baffles me, but her writing is superb. (And she has a livejournal!)
I’ve read the first two and, unlike most people, thought the second book better than the first. I think they are very worth reading, both for the great humor and the fact that the “hero” pretty much needs smacked. My husband read the first and couldn’t stand the hero (not the djinni, the boy), so it’s possible to be really turned off by this series.
Bruce Sterling - founder of Cyberpunk, but more than that. His Shaper mechanist stories turn classic SF tropes on their head. His Islands in the Net is still the best near-future extrapolation I’ve ever read. And I’ve read quite a few. His non-fiction Hacker Crackdown is fantastic as well.
Cordwainer Smith - when he’s good he’s extraordinarily good. When he’s bad, he’s a little ponderous but still interesting.
Elizabeth Moon’s The Speed of Dark kicked me in the guts - in a good way.
Has Orson Scott Card been mentioned yet? I like his early stuff, but I’m behind on his more recent work.
Another vote for Greg Keyes, Lois McMaster Bujold, Robin Hobb, George RR Martin, Garth Nix.
I’ll add Elizabeth Haydon (Rhapsody and its sequels), Robert Sawyer (a Canadian!) (Hominids and its sequel Humans, among others), Audrey Nieffenegger (if her stuff isn’t in the general fiction, that is), and Naomi Novik (her new series, beginning with His Majesty’s Dragon, is one of the most interestingly done fantasty series I’ve ever read that involved dragons. Totally unique).
Terry Pratchett’s stuff is often shelved in sci-fi/fantasy.
David Weber - I prefer the Honor Harrington series, but he has some fantasy stuff as well as an alternative history series with David Flint Diana Wynne Jones has good stuff; I particularly like her send-ups of the fantasy genre: Dark Lord of Derkholm and The Toughpick Guide to Fantasyland. Esther Friesner is also very good, especially the Chicks in Chainmail series.
I don’t know how you feel about short stories, but I love anthologies, particularly anything edited by **Denise Little ** or Martin H. Greenberg.
unfortunately, he’s pretty much out of print. NESFA Press has the Collected Works of Cordwainer Smith and Norstrilia , along witth their Cordwainer Smith Concordance. The first two are pricey hardcovers, and not likely to be big sellers, especially to a young audience unfamilar with him (even if I think more people ought to read him).
I could say the same about a lot of other authors – Hal Clement, Fredric Brown, William Tenn, Eric Frank Russell – which is why I did’t recommend their books, even though I think they’re all great.
I forgot Naomi Kritzer and Laurie J. Marks. I recommend Kritzer’s Fires of the Faithful which has an interesting take on religion and complex world building. The Freedom trilogy is now complete, but I haven’t finished it yet.
For Marks’, I believe Fire Logic and Earth Logic are the only books still in print. Still, I like her world building.
Both have lesbian themes, which may or may not be a plus, depending on your clientele.
Oh, and no one’s mentioned Jacqueline Carey yet? Definitely the Kushiel series and she just started the second trilogy.
The Kushiel series, I think the author’s name is Jacqueline Carey. She just started a spin-off series. This is also a nice cross-over with errrr, romance, bondagey-romance whatever. I don’t really read it for the sex, myself.
Jonathan Strange & Mr. Norrell, which I think is out in paperback now (Susanna Clarke).
OOOHHHH, and my recent fave, which is a great cross-over with Young Adult, is Libba Bray’s Victorian-Fantasy-Enid Blyton ripoff trilogy-it starts with A Great and Terrible Beauty and continues with Rebel Angels.
I have Kushiel’s Scion out from the library right now :D. We carry the first trilogy. We’ve got some Mercedes Lackey, but not a lot. The kids’ section has tons of great stuff- Paolini, Tamora Pierce, Diana Wynne Jones, Michael Ende, Stroud, a little Madeleine L’Engle (I’m pushing for more), Pullman, Nix… it’s really good. I just got the isbns for the adult editions of the Old Kingdom books, and I’m going to jump up and down on my manager until he orders them.
A friend just lent me a Lynn Flewelling series that very good. The first book is Luck In The Shadows. Oh! Barbara Hambly! Must get some of her stuff!
I’ve read Alphabet of Thorns, but no other McKillip. I liked it a lot. We’ll have to get some of her books. Is the Deryni series (Kurtz) good?
Try Towing Jehovah by James Morrow, or the His Dark Materials trilogy, if you have a sense that your customer is NOT looking for fantasy with a Christian theme.
She got on my “best authors” list for The Book of Atrix Wolfe, but that’s another good one. Haven’t read Alphabet of Thorns yet. Of course, the Riddle-Master of Hed trilogy is her classic, although possibly only in print now as the omnibus.
The Deryni series (Kurtz) is pretty good, for a run-of-the mill extended fantasy series. About on a par with Eddings, although a different style. Better than the Shannara books, anyway.
Judith Tarr also has some pretty good pseudo-historical fantasy novels that are in print.
All the ones I was going to mention have already been mentioned (be sure to get Jonathan Strange and Mr. Norrell, with its very high crossover appeal!), so instead I’ll mention some resources:
-The Year’s Best Fantasy and Horror collections are chock full of great genre stories, with a very liberal definition of genre. Even better, there’s always an extensive essay in teh beginning of th book reviewing the most notable fantasy books to ahve been published in the previous year. I’d think this essay is a must-read for someone stocking the shelves of a fantasy section.
World Fantasy Award Winners: if you’re not sure which books to order, you could do worse than to go over these recommendations. I don’ tknow how they map to sales, but they tend to recommend very high-quality books (even if the best one doesn’t always win ). You might consider posting last year’s nominees and winners, or a list of all winers for the past 20 years or so, next to the section, as long as you can keep the books in stock.