Francesco, your idea for using shopper program for movies I want to buy is a good one. I have Splashshopper and I can type my Amazon wishlist in it which will help a lot. For some reason I never thought of using it that way. But it solves part of the problem.
As far as a DB of what I already have: I messed around with a freebie called Media Database
http://www.kaseisoft.com/in.html today. It might work, but I may continue looking as I'm not getting the desktop data to work with the handheld. I think I will continue looking for something.
Hacker, I agree with Francesco, that is a pretty important question and deserves some consideration.