This is far from an exhaustive list, but is intended to give some idea of the diversity of English-language outlets and publications covering STEMM for a general audience. Outlets known to pay for freelance commissions marked with an *. (For a truly exhaustive list, including contacts, word rates, fact-check status etc, checking out this amazing resource from reporter/NYU journalism lecturer Robin Lloyd.)

General science ~ Life sciences ~ Physical sciences ~ Health and medicine ~ Environment ~ Technology

General science

• Aeon * (but does not accept unsolicited pitches)
• Atlas Obscura * (pitching guidelines are here)
• Australian Geographic * (editorial contact is here)
• Australia’s Science Channel
• BBC Focus magazine (information on pitching is on their contact page)
• Christian Science Monitor * (contributor guidelines are here)
• Cosmos *
• Discover * (submission guidelines are here)
• Eos * (pitching advice here)
• Fast Company
• Gizmodo *- includes io9 and Earther (pitching guidelines here).
• Inverse *
• JSTOR Daily * (submission guidelines are here)
• Lateral * (pitching guidelines are here)
• leapsmag * (contact details are here)
• MIT Technology Review * (pitch information is here)
• National Geographic  * (pitching instructions here)
• Nature (see also Nature News and Nature Index)
• Nautilus * 
• New Scientist * (guide for freelances is here)
• Noema *
• OpenMind *
• Popular Science * (and here’s an article on pitching to them)
• Quanta Magazine
• SciDev.net * (pitching guidelines are here)
• Science * (freelancer guidelines are here and contacts for their news staff can be found here)
• ScienceAlert
• Science News *
• Science News For Students * (advice on pitching is here)
• Scientific American * (submission guidelines are here)
• Slate * (pitch guidelines are here)
• Smithsonian Magazine (pitching form for the website is here, the magazine is here, and here’s an article from the Nieman Storyboard on what SM is looking for in a pitch)
• Undark * (submission guidelines are here)
• Vox * (submission guidelines are here)
• WIRED and WIRED UK * (here’s a piece from Quora on pitching and a post on pitching to WIRED UK)

Life sciences

• Asimov Press * (pitching guidelines are here)
• Audubon * (submissions guidelines are here)
• bioGraphic * (submission guidelines are here)
• Hakai * (submission guidelines are here)
• Sapiens * (pitching guidelines are here and here)
• The Scientist * (and here are their pitching guidelines)

Physical sciences

• Air & Space Magazine * (writers’ guidelines are here)
• Astronomy * (submission guidelines are here)
• Chemical & Engineering News 
• Chemistry World (editorial contacts are here)
• MRS [Materials Research Society] Bulletin * (pitch on materials research stories to newseditor@mrs.org)

Health and medicine

• British Medical Journal * (contact for news editor is here)
• Eating Well * (pitching guidelines are here)
• Elemental * at Medium (editorial contacts are here).
• Men’s Health UK * (great pitching guide here)
• Mosaic * (pitching guidelines are here)
• Psychology Today * (pitching guidelines are here)
• Stat

Environment and sustainability

• Anthropocene * (pitching guidelines are here)
• Bloomberg Green
• Cipher *
• Earth Island Journal * (pitching guidelines are here)
• Ensia * (submission guidelines are here, and Ensia also runs a mentoring program that pairs less experienced writers with a mentor to work on a specific piece)
• Environmental Health News
• Greenbiz (pitching advice here)
• Green Matters * (pitching guidelines are here)
• Grist * (pitching guidelines are here)
• Mongabay * (pitching opportunities are here).
• Orion Magazine * (pitching guidelines are here)
• Sierra Club * (editorial guidelines are here).
• The Revelator * (pitching guidelines are here, and here’s a recent call for pitches)
• Yale Environment 360 * (submission guidelines and contacts are at the bottom of this page).

Technology

• Ars Technica
• CNET
• Futurism *
• Geekwire
• Motherboard * (pitching guidelines are here)
• The Verge * (pitch guidelines are here)