Cosmic Horror Monthly, an online horror and dark science fiction magazine, is in search of flash fiction in the genres of cosmic horror, dark science fiction, and weird (that last one is specifically open to interpretation). 500 words tops, and follow submission instructions. While you're at it, get a free subscription, if horror is your thing... in which case you should also check out their regular (non-flash fiction submission page. Flash fiction submission (only) is open monthly from the 1st to the 7th. Win up to $100!