PodCastle; The Fantasy Fiction Podcast; buys fantasy, magical realism, urban fantasy, slipstream, high fantasy, etc.
Escape Pod buys science fiction.
Pseudopod buys horror.
generally 2,000-6,000 words for short fiction – pays $100
some flash fiction up to 1,000 words – pays $20
Info on how to submit to any of the 3 is HERE: http://podcastle.org/guidelines/