In publishing, as with all businesses, it is "brand recognition"that counts, and some of the names on this list are very well known.
If you don't know where to start, I would recommend beginning with Pyr.
3 Major Science Fiction and Fantasy Publishers Accepting Unagented Manuscripts
Top 5 Sites for Science Fiction Writers
Angry Robot normally accepts submissions via an agent, but every so often they have an open submission month. They are currently OPEN.
What they are looking for: SF/F "and a little pinch of WTF." Note that they are looking for full-length novels, not short stories, novellas, epic poems, comic book scripts, etc. Angry Robot books are aimed at adults, so no middle grade or young adult themes at this time.
Terms: Competitive advances and royalties. English print versions in the UK, US and Australia plus region-free ebooks globally.
Back Hall Press
Back Hall Press is aimed at niche markets.
What they are looking for: All subgenres including speculative, dystopian, apocalyptic, and dark fantasy stories. Unconventional concepts, world-building and diverse characters are always a plus.
Terms: Authors receive 30% of profits on their titles, paid quarterly. They do not pay advances. Specific details on rights, royalties and payments will be discussed before any agreements are signed.
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."
What they are looking for: Urban fantasy / paranormal fiction only, with a strong focus on series — no standalone titles. Books may fall within the categories of paranormal romance, mystery, thriller, fantasy, horror, and/or teen fiction
Terms: "We buy World rights… and we give them all back to you in 3 years if you ask us to. We publish your books in a reasonable time (no 18-month wait here). We offer a $200 advance, along with an extremely competitive royalty percentage (40-50%). We create e-book and paperback versions of all our full-length books, and are working on attaining paperback distribution. Our novellas and short stories are e-book only. We only take on books and authors we believe in."
"We are a micro-niche, nano publisher currently slated to offer about 10 titles a year. We are based upon a collective structure that enables editors to personally select projects and become Project Leads as the editor in charge. This means that starting with your acceptance, you'll have one person that is completely invested, from editing, through design and into publicity, in your project."
What they are looking for: "Books worth burning." Dark Fantasy, Steampunk, Urban Fantasy.
Terms: Montag Press retains a 70/30 share (net) with the author for worldwide primary and secondary rights including digital, options, film and video production, and print rights, which is exclusive for 10 years from the date of publication.
Pyr is the scifi and fantasy imprint of Prometheus Books. They have international distribution.
Terms: Advance, plus royalties.