A Few Things to Get You Started...
If you're new to filming documentary style or have been at it for awhile, here are a few resources that will come in handy.
Kino-Eye is a comprehensive blog with tips ranging from sound, to lighting, to film recommendations.
An excellent place to ask questions and learn from other production artists is on student filmmakers forum.
Ira Glass of This American Life is one of the great modern day storytellers. His manifesto on storytelling is a must read for anybody attempting a documentary and you can find it at Transom, along with audio support.
If you're planning to add music to your films, be sure that you have the full rights. Here are a few places you might want to search for soundtracks:
Freeplay Music: www.freeplaymusic.com
The Music Bakery: www.musicbakery.com
Royalty Free Music: www.royaltyfreemusic.com
Idealist.org provides a comprehensive list of non-profit organizations that can be searched by focus area and location.