A 6-day documentary festival organised by the American Film Institute (AFI) and Discovery Channel in Washington DC for 22nd - 27th June 2010.  Submission deadline 12th March 2010
The previous Sliverdocs Festival attracted some 25,000 attendees and more than 100 films from 60 countries.

Important Deadlines to know when submitting your film(s):
   Regular Deadline for Submissions is March 12, 2010
   Late Deadline for Submissions is March 19, 2010

The organisers encourage film submissions through Withoutabox.  This is an online entry process: fill out one master entry form and then have full advantage of quick entry and extended deadlines for a number of festivals.