Free GM Resource: Libib
It has been my experience that most of us couldn't remember every item in our collection and since most of us also have a limited budget, doubling up on some items means we don't have the resources to pick up new things instead.
Not so much with RPGs, but in the last few months I can think of three separate occasions where I picked up a new movie that I already owned. Returning the ones I could return was a bit of a PITA.
This is where Libib comes in. Libib is an online database that lets you keep track of your media collections. You can add stuff through a bar-code reading app, do an online search, or just add stuff in manually. You can publish the collections online if you want, which means that anywhere you have access to a web browser you can see what you have in your collection. The free version is quite robust as it isn't really a feature-limited (or size limited, as in only cataloging 100 items, but technically there is a free limit of 100,000 items...I can live with that) and if you needed the paid version, which included things like generating your own item bar codes or managing lent out items, the service is $5 a month.
Libib is a great option for helping manage your collections, not just the RPG stuff.