%windir%\ie7updates
%windir%\ie8updates
%windir%\SoftwareDistribution\Download
Previous versions of Java (java didn't do an uninstall from versions earlier than 1.6.x or so so many 60-100 meg copies sit there in %ProgramFiles% )
Remnant files in the "[drive letter]:\Recycler". Deleted files that dont cause the icon on the desktop to show as "i've got deleted files" but can be identified by such programs as Treesize.
Service pack uninstall folder in %windir%..once you've finally decided your REALLY not going to go back to XP service pack 2.
Itunes installers in "<user>\Application Data" folder. Seems whatever user is logged on and does the itunes update the installer gets put in their user profile folder.
Hmmm...maybe this should have gone into suggestions.