The easiest way to see the whole span, Mike, is through the Administrative tools - Computer Management - Local users and groups - Users.
On the few occasions when I have had to clean up in that area, I have always found deleting the "unknown" ones seems not to do harm. Any others can only be based on your personal knowledge of where they came from.
It is a good idea to disable any doubtful ones first, through right clicking "properties" It, at least, gives you the opportunity to re-enable if things go awry!