Here's my filing system currently... I have three things I use.
#1 I use an accordian file (pictured here) that I take with me to crops. It has sections for holding info: re: MW Express kits, Order forms, checks/cash, orders received, customer contact info, some articles I've printed re: basics of scrapbooking, etc to give out to people who ask, that kind of thing.
#2 I have files in my filing cabinet (also pictured) for 2007 receipts, bank statements, credit card statements, customer contact info, completed orders, orders in progress, tax documents, customer wish lists, etc.
#3 I have my MW binder, which houses the current catalog, printouts of all the .pdf files on the MW business cd, and the cd itself.