I'm a big fan of short stories.
I've released one short story by itself, and plan to do a few others the same way. I've no sales on the single short story, but it's only been 2 weeks.
I've also released a collection of flash fiction. That's actually sold a handful of copies in the few days it's been available. I plan to do more of those too.
I'm new at this ebook thing, so I'm experimenting.