I also created an Excel spreadsheet. I started it just for my SU! stuff but then decided to list everything in my craft room for insurance purposes. I have a tab for the following:
SU! sets/wheels - Name, Product #, Price, Hostess set or not, Catalog, Page, and Year that it retired
Inks/Coloring Implements: Name, Product #, Price, Company, Catalog (if in one), Page, and Year it retired
Non-SU! stamps: Name or description, If it is a set or not, How many images, Price, Theme, Company, Catalog, Page
Books/Magazines: Name, Date, ISBN #, Price, Theme, Company
Tools: Description, Price, Theme, Company
The prices I listed were what it would cost to replace the items (if possible) not what I actually paid for them due to my SU! discount and coupons/sales for Non-SU! stuff. I will not tell you how much it added up to but my husband was a bit shocked.
I do not keep an inventory of consumables (papers, embellishments, yarn, etc.)
The hardest part was putting everything in to begin with it. Very time consuming, but I would just bring a catalog or a stack of items and enter the info. If I didn't have a price or name, I'd look on the internet at company websites or do a search for the item to find info on it. Now when I buy something new, I immediately put it in the spreadsheet before taking it to my room.
Best of luck on finding and inventory process that works for you.