One of my favorite markets to read and submit to is Every Day Fiction, a web zine of daily flash fiction of all genres and types. In fact, the first story I had "go big" was on EDF, a flash piece called "Security Question." The feedback they offer on submissions, even rejections, is very valuable, and the editors there are great to work with. The readers are also engaged, and love to leave comments (good and bad), which is wonderful for a writer.
Sadly, EDF suffered some technical problems in 2015 and was been unable to accept new submissions for a while.
Happily, they just announced they've fixed the problem and are open for business again! If you write flash fiction, make sure you are submitting to EDF. Follow them on twitter as well at @EveryDayFiction.
If you like bite-sized reads, bookmark them and check it out every day. You won't be sorry!
Welcome back, Every Day Fiction!