DVD Collection Tracker
Program to aid online catalog/database of personal DVD collections.
http://www.dvdtracker.com/

DVD Profiler
Software for cataloging DVD collections. Features, downloads, FAQ, and forum.
http://www.dvdprofiler.com/

DVDLender
Service for creating online DVD lists and lending, borrowing, and trading with others.
http://www.dvdlender.com/

DVDExchange-Online
UK-based site allowing members to trade Region 1 and 2 DVD movies and games.
http://www.dvdexchange-online.co.uk/

Mediachest.com
Lets people inventory their collection of DVDs online and then search through their friends and friends of friends to find DVDs to borrow.
http://www.mediachest.com/