Sometimes if feels silly to list well-known and hugely popular markets here, but it's possible you've not considered the challenge of being published in Clarkesworld Magazine. So here it is:
Clarkesworld is a monthly science fiction and fantasy magazine first published in October 2006. Each issue contains at least three pieces of original fiction from new and established authors. Our fiction is also collected by issue in signed chapbooks, ebook editions/subscriptions and in our annual print anthology, Realms.
As for some indication of what they like:
Science fiction need not be "hard" SF, but rigor is appreciated. Fantasy can be folkloric, medieval, contemporary, surreal, etc. Horror can be supernatural or psychological, so long as it is frightening. There are no barriers as to levels of profanity, gore, or sexuality allowed, but high amounts of profanity, gore, and sexuality are generally used poorly. Be sure to use them well if you do use them.
There is a also great list of ideas on the submissions page, politely marked 'the following are likely hard sells'. I believe a good translation of this is, 'please do not send us these kinds of stories'. You might like to peruse the list to get a feel of what everyone must be sending them. It's always helpful to get some idea as to what sort of done-to-death concepts are floating out in the submission-sphere.
The magazine accepts 1,000-8,000 word SF and Fantasy fiction, with a preferred length of 4,000, and pays 10c per word up to 4,000 words, dropping to 5c per word after that.
Full submission guidelines here, folks: http://clarkesworldmagazine.com/submissions/
PS: Clarkesworld Magazine has a really great post here analysing statistics of readership, traffic and submissions. I really love these sorts of posts.
PPS: If you want to support an excellent publication, click through to their donations page and help out.