Reducing size of Windows 7's WinSXS folder

To reduce size of your \Windows\winsxs folder, run this in command prompt as admin: 

dism /online /cleanup-image /spsuperseded /hidesp

This will get rid of extra files which have been superseded by a service pack update. If you installed using a slipstreamed installation (in other words, it already had a service pack integrated when you installed Windows) you should use this command (replacing D: with the drive your Windows folder is installed on):

dism /image:D: /cleanup-image /spsuperseded /hidesp