As an occasional writer and frequent reader of drabbles (exactly 100-word stories), I don’t think there can be any doubt that Martian magazine hosts the best of the form. They’re a web-zine that has published a science fiction drabble every week for the past year, and they pay authors professional rates. If you prefer your drabbles in themed anthologies, they’re doing that too!
Now, they’re running a Kickstarter to fund their second year, with hopes of expanding. They have all manner of physical and e-book rewards available. I don’t have any skin in the game—I just like what they’re doing, and I’d love to see them get to do more of it.