I copy every installation package along with emails, vendor web pages, install logs, etc. that are related into a dated folder (eg: '2012-09-21') on one of my drives.
I never back up that drive, it is usually a 'write-only' device.
Then I copy that data to a second identical drive which is also not backed up.
PS: to make a right click 'make folder date' command for Windows Explorer:
[HKEY_CLASSES_ROOT\Directory\shell\Date_Folder]
@="New folder with today's date"
[HKEY_CLASSES_ROOT\Directory\shell\Date_Folder\command]
@="cmd.exe /c md \"%1\\%%DATE%%\""
I think the date format is region specific - mine is set to yyyy-MM-dd in 'Region and Language' control panel.