Today's market is the monthly Lightspeed magazine:
[...] an online magazine focusing exclusively on science fiction. In its pages, you will find all types of science fiction, from near-future, sociological soft SF, to far-future, star-spanning hard SF, and anything and everything in between. No subject is off-limits, and we encourage our writers to take chances with their fiction and push the envelope.
Submissions are made through their online system (I believe it's the Clarkesworld submission system), and guidelines are here: http://www.lightspeedmagazine.com/about/guidelines/