Holly Lisle is putting together a new sort of online magazine project based primarily around serials, although with some shorter one-shot stories too, and with issues grouped into "seasons." She explains it better than I do. :) Anyway, it's called Rebel Tales, is starting off as an F&SF market, and she has the preliminary writer's guidelines up.
The guidelines are worth reading even if you don't plan to submit; she has a refreshingly blunt, take-no-prisoners attitude toward people who submit without following instructions, or without being able to write terribly well, or without knowing what SF or Fantasy actually are, or even what a story is. I got a few chuckles while reading.