My story "Chaos Theory" was sold to online magazine Darker Matter. It appeared in the fourth issue. I was paid in advertising space, which I traded to my friends at Shimmer Magazine for some copies.
Alas, Darker Matter published issue #5, then died. It lingered online for a year, but it is now no more. A shame. Although I made a mistake with the story by starting with a needless infodump, the story rewarded the folks who muddled through the infodump and got to the meat of the story. It was actually the brightest story in a magazine dedicated to mostly dark fiction. That says something about the concept.
It's a shame that most aggressive online magazines fail after a year or so. It's difficult to pay professional rates out of an editor's pocket, and unfortunately, most of them don't have a positive cashflow.