I use Excel for all my stuff. I have one for hair stuff, skin stuff and I'm working on the one for my makeup. I use one book for each stash and then a different sheet for each category.
For example, in the hair stash book, I have shampoos on the first sheet, conditioners on the second sheet, and styling products on the third. I keep everyting listed in alphabetical order by the brand and I update it when I finish something or buy something new.