I freed about 1 GIGABYTE of data just by deleting my old graphics card drivers
Information:
"Starting with Windows Vista, the driver store is a trusted collection of inbox and third-party driver packages. The operating system maintains this collection in a secure location on the local hard disk. Only the driver packages in the driver store can be installed for a device."
http://msdn.microsoft.com/en-us/library/windows/hardware/ff544868(v=vs.85).aspx
"I was asked this recently and I thought it was an interesting question:
I know I cant delete things out of the component store, but what about the driver store? Can I remove files from there without hurting anything?
The answer to this is: YES."
http://blogs.technet.com/b/joscon/archive/2010/09/15/so-what-about-the-driver-store.aspx