Tor.com
http://www.tor.com/page/submissions-guidelines
Tor.com welcomes original speculative fiction short stories and poetry. We define "speculative fiction" broadly, including SF, fantasy, horror, alternate history, and related genres. We're particularly interested in stories under 12,000 words. We pay 25 cents a word for the first 5,000 words, 15 cents a word for the next 5,000, and 10 cents a word after that.
BUZZY MAG
http://buzzymag.com/submissions/
Buzzy Mag is looking for original science fiction, fantasy and horror short stories up to 10,000 words. Thriller, suspense and paranormal tales that cross into traditional speculative fiction are welcome. Buzzy accepts submissions from both authors and literary agents. Make sure you short story is acceptable for a 15-year-old to read. We DO NOT ACCEPT pornography, child subject matter, racial propaganda or fan fiction. Payment is ten cents/word.
This next one's pretty neat because they accept previously published stuff...
COLLIDOR
https://collidor.submittable.com/submit
Collidor is a science fiction appzine. We seek character and relationship driven stories from the full gamut of subgenres of speculative fiction, as long as there is a scientific or technological element that reflects the existential conditions for life forms and consciousness (human or otherwise). We are unfortunately not accepting horror, pure fantasy, vampire or zombie themed stories unless they meet the above criteria. We are accepting pitches for essays, reviews, opinion pieces and editorials that would be of interest to our readers. Topics include science, technology; book, movie and game reviews; geek/fandom culture, interviews, artist profiles and event coverage. We pay $0.25 per word for the first 5,000 words, $0.20 per word for the next 5,000 and $0.10 per word up to 18,000 words. We pay $0.11 per word for serialization rights for the entire series. We pay $0.10 per word for previously published stories.