I don't bother with a separate spreadsheet for each company, I simply add notes to my master "My List of Companies" sheet. Companies come and go, get bought out, change their names and have other changes. My list includes every company I have ever attempted to sign up with as well as those I have heard of and a note as to why I decided not to register with them. There are many lists of companies out there on the web that are no updated, some of them are ones I copied off back in 2003-2005 and half the companies are gone or have changed names. So when I see 'Shop 'n Check' on my sheet, it tells me that it became Market Force, so it is not still another company to research and see if I want to sign up.
The spreadsheet includes user name and password, address for the log in to their job board, date I registered, phone numbers, addresses, scheduler names, payment cycle, how they pay, etc. I no longer keep it carefully up to date, though I do refer back to it when I get an email from a company I don't remember registering with and certainly when shoppers I have grown to respect have issues with a company, that gets noted on my sheet along with the approximate date of the issues.