I am doing a Flash Fiction panel at OmniCon, so I thought I should post some flash market links. This list is by no means complete and does focus on genre fiction. For a more thorough search, try duotrope.com.
Daily Science Fiction: (SF & F) They run flash (loosely defined) Monday through Thursday and a longer story on Friday o get you through the weekend. And they pay 8 cents a word, good money for fiction, but it’s free to get the stories emailed to you and/or read them online.
Analog: (hard SF) Their “Probability Zero” section is flash fiction.
Beneath Ceaseless Skies: (F) A very well respected fantasy zine that buys flash.
Every Day Fiction: (SF/F/H) This is run by a friend of mine and has bought a few stories from me. Low pay but a lot of readers. Read it online for free.
Flash Fiction Online: (SF/F/H) All flash, all the time.
10Flash: (check issue themes) 10 themed flash stories per quarter.
Abyss & Apex: (SF & F) A well respected semi-pro zine that buys flash.
Untied Shoelaces of the Mind: (SF/F/H) Buys stories 2000-words or less. They bought my Pied Piper/zombie story “Not Rats” for their anthology, so I wanted to include them.
There are lots more out there, and new ones seem to pop up regularly.
Scott W. Baker .net 
Thank you Scott—this was a helpful post! Happy holidays.