http://dcuo.mmorpg-life.com/tag/briefing/ This site hasn't failed me yet when doing my briefings. They have some great information on where to find them including a screenshot of the mini map, and 3-4 other screen shots of the surrounding area. I have scanned through it and there are a few incomplete briefings that they have not found yet.
http://dcuniverseonline.wikia.com/wiki/DC_Universe_Online_Wiki I have yet to use this site, but was told it is great and that they always have a lot of information, and with it being in a wiki it should always be updated.