It really helps when I'm crafting a card and deciding what to use without dragging out each cartridge to look at them. I used the cover of the Cricut Manual for my binder cover to distinguish from my other binders on my craft bookshelf.
Easter 2010 Cartridge
Mother's Day 2010 Cartridge
I also have a sheet showing the different sizes of shapes for fitting reference. I used my cricut marker to draw shapes in various sizes from each cart.
I also printed out a cartridge list from my cricut account page. I copied and pasted the list into a Word document and sorted it alphabetically for faster and easier reference of my cartridge inventory.