Useful Links

Briefings and Investigations Database with Pictures
http://dcuo.mmorpg-life.com/

DCUO Source Skill Planner/Build Calculator
http://dcuosource.com/skillplanner/

Item Database (very incomplete)
http://www.dcuocentral.com/

2nd Item Database (also very incomplete)
http://www.exobytedata.com/

3rd Item Database (mainly higher level items)
http://www.dcuo-db.com/

Item Drop List (for PS3, majority is correct though, we just don't have hard mode of the easy instances)
http://community.us.playstation.com/thread/3411307?start=0&tstart=0

DC Official Forum Guide/Question Subforum
http://forums.station.sony.com/dcuopc/forums/show.m?forum_id=71

Collections Guide from Official Forums
http://forums.station.sony.com/dcuopc/posts/list.m?topic_id=26399

Legends PVP Movesets
http://forums.station.sony.com/dcuopc/posts/list.m?topic_id=18937

It's a shame a lot of the loot databases are so incomplete. It's making it hard to find certain drops needed to complete styles.

Yeah, dcuo-db.com is the most recent and the most updated, but it's also much more focused on hero-side drops than villain-side ones. I blame the lack of an automated system which can simply read off of a log.