Windows only: If you're looking for an all-in-one portable application to keep tabs on all your stuff, myCollections is a lightweight organiser you can use to keep your collections orderly.
While some products catalog books and movies, or just music or games, myCollections covers a broad spectrum by providing cataloging categories for Apps, Books, Games, Movies, Music, Television, and XXX. Also, oddly enough, there is a distinct category for Nintendo DS games—apparently the software's author is a big fan of the system.
myCollections pulls from a variety of databases—make sure to go into the options and uncheck the French-centric sources like Amazon.fr unless you want French results in your searches—covering software, music and more. Everything we searched for was found, but myCollections does seem to be particularly sensitive to partial searches. You can't throw a partial search out and pick from a list of potential matches you need to search for the actual title, i.e. "The Curious Case of Benjamin Button" not "Benjamin Button".
Although the manual search is functional if a bit anal-retentive about how you use it, where myCollections really shines is the ability to scan your directories. If you have a directory of movies for instance you can automatically scan it for titles and myCollections will even read the .NFO file, if available, to populate the entry for the movie.
If you're focused mainly on cataloging your movie collection, make sure to check out the hive five on the topic. myCollection is freeware, Windows only.