Make a Spreadsheet or database with Office or Access (or Openoffice, for free software).
There are software that specifically does DVD cataloging but online versions risk the 'going-out-of-business' thing while most other offline software has limits unless you pay.
If anyone is using a good free one, I'm also interested.
Currently, I track it on my Palm with JFile and a custom database. So that I had it with me whenever I shop...