Identifying stale data

Our management asked us to identify “stale data” on our servers – most of which running either server 2003, server 2008 and some still win2k. By stale they refer to data that is no longer necessary for business purposes/and/or is no longer being accessed (with stats to back this up).

My initial reaction to this was number 1 would probably be ex employees home drives still resident that weren’t manually deleted as part of the leaver process. I have also identified many people disabled in AD who should have been deleted – and subsequently their mailbox stays in exchange servers (but again per person its only 40mb each).

I am really after a full comprehensive list of what kinds of data / types of files/devices could still be out there taking up valuable space – and best ways to identify this problem. As windows admins any input welcome.