linux.com has had articles about a couple of media collection programs called gcstar and data crow. They're similar in concept: both are databases for your CDs, DVDs, books and such. Each allows you to enter your collections with searches of amazon.com, imdb.com, etc. So if you have a copy of X2 on DVD, you can type 'X2' in the search field and it'll retrieve the cast list, cover art, plot summary, and other stuff.
gcstar is built on Perl and gtk2, and data crow is built on Java. So both are more-or-less cross-platform (they run on Linux, Windows, and probably OS X).
Both also allow the user to add loaning information to records. If you loan your copy of X2 to someone, you can make a notation of that as part of the X2 record. And both let you import and export your data (gcstar seems more flexible in this regard, in that it supports a fairly wide variety of formats).
I've tried both, and I'm finding gcstar to be more reliable. data crow is pretty crashy, and I gave up on it.
Some drawbacks to gcstar are that you can only select one item from the results of a search. If you have several Star Trek DVDs and you run a search for 'star trek', you can only select one of the search results to add it to your collection (you have to run a separate search for each Star Trek DVD you own). It would be nice if you could do Ctrl-click to pick Wrath of Khan and The Undiscovered Country if they both show up in the search results (data crow actually lets you do this).
And gcstar also has gtk tooltips which pop up when you mouse over the items in your search results. These tooltips sometimes make it hard to click on the search result that you want.
And it seems that the current version of gcstar (v1.1.1) is less than completely compatible with the version of the Gtk2 Perl module currently available in CPAN (v1.142, 21 January 2007). To make it work, you have to comment out the set_row_separator_func() and set_focus_on_click() calls in a couple of gcstar modules. Lame.
I actually prefer the data crow interface, but it kept hitting out-of-memory errors. I had to restart the application pretty frequently. That was beyond annoying. So for now I'm using gcstar.