These might be of interest - I can't vouch for the organisers, but they may be worth a look at least:

LIGONIER VALLEY WRITERS FLASH FICTION CONTEST
http://www.ligoniervalleywriters.org
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NO ENTRY FEE
Ligonier Valley Writers is looking for flash fiction about
zombies for its Flash Fiction Contest 2008. Deadline
August 21. Flash fiction stories must be less than 1,000
words long. The first-prize winner will receive $50, second
prize $25, and third prize $15. Send two hard copies of
your story to Ed at 409 Ninth St., New Florence, PA 15944
and email it as an attachment (in Word or RTF) to
ed.kel@verizon.net. All winning entries will be published
online at LVW's website. The theme is always something
scary (last year vampires, in 2006 ghosts, etc.) because
the winners are also read aloud at the Haunted Weekend at
West Overton Museums in Scottdale, Pennsylvania, on the
Friday, Saturday, and Sunday before Halloween (October 24-
26). Humorous scary stories are always welcome.

And...

HOTTEST FLASH FICTION CONTEST
http://mwgcontests.org/
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$10 ENTRY FEE
Deadline September 15, 2008. Word limit 1,000 words.
First place $100, second place $50, third place $25.