On average we manage more than 1000 domain name for clients at multiple registrars. In order to track renewals and just as important, "Do Not Renews," we developed this sheet for ourselves. It aggregates the current domains lists from each registrar and then allows us to sort and filter on domains that need to be renewed. It also allows us to flag domains that are to expire on purpose.
Note that the image is blurred on purpose to protect the data.