• Flash Fiction Online
• Lightspeed Magazine
• Strange Horizons
• Daily Science Fiction (get it in your inbox)
• PodCastle (audiozine)
• Escape Pod (audiozine)
• Uncanny Magazine
• Clarkesworld Magazine
• Tor.com

Not free but worth every dime:

• Magazine of Fantasy&Science Fiction
• Asimov’s Science Fiction
• Analog Science Fiction and Fact
• Interzone
• Intergalactic Medicine Show
• Andromeda Spaceways Inflight Magazine
• Space & Time Magazine