Here are four science fiction and fantasy publishers that don't require an agent. Several offer competitive advances and royalties.
In publishing, as with all businesses, it is "brand recognition"that counts, and some of the names on this list are very well known.
Mega-List of Science Fiction and Fantasy Magazines - Paying markets
Top 5 Sites for Science Fiction Writers
Small Canadian press.You do not have to be Canadian to submit your work, they accept manuscripts from any nationality worldwide. They have a distribution throughout North America.
What they are looking for: Science Fiction and Fantasy between 75,000 and 100,000 words. Adult audience (20 and up).
Terms: Advance and royalties. "We rarely ever negotiate the royalty percentages and/or advances that we offer, and if we do so, then only with previously published writers."
Aetheon is open to all genre fiction, with a focus on Science Fiction and Fantasy. "We don’t care what sub-genre you write in. Hard Sci-fi, Epic Fantasy, Space opera, Military SF, Alt/History, Time Travel and more." Aetheon does not offer an advance, though they do give royalties. Books are published in all English-language territories – notably the US, Canada, UK and Australia – and are distributed through Ingram. Length should be between 60,000 and 80,000 words. Read their guidelines here.
Send the manuscript as a single file (do not break it into separate chapter files). The form only accepts a single file so any synopsis and contact info needs to be in the file with your manuscript.
Your submission must include your name, email address*, postal mailing address, and telephone number on both your cover letter and the first page of the manuscript. *[If you have an alternate permanent email address, please include it, in case your primary account goes out of service.] Include a plot outline if possible.
Jo Fletcher Books
Jo Fletcher Books (UK), part of the Quercus family, publishes science fiction, fantasy and horror, including all subgenres. "JFB authors are writing critically acclaimed, award-winning and unputdownable novels right across the fantastical spectrum, encompassing everything from crime to literary fiction. If you love chunky, engrossing epic fantasy or fast-paced dystopian thrillers, alternate history or paranormal romance, far-future SF or mythic fantasy, spine-chilling horror or heroic fantasy, you’ll them all here: just step through the portal into the wonderful worlds of Jo Fletcher Books."
Submissions: In addition to adult science fiction, fantasy and horror, Jo Fletcher considers YA, but only if it can be classed as YA/Adult crossover. Previously self-published books are accepted, as long as the author is willing to let all rights revert to JF on signing a contract.
See their guidelines here.