Another folder which can take up a lot of space is the c:\windows\winsxs folder. This contains files added by service packs and patches. If you are prepared to lose the capability to roll back to pre patch and service pack status then a lot of space can be reclaimed. In my case I got 8 Gb back.
In Windows 7, the DISM /online /Cleanup-Image /SpSuperseded command at an elevated permissions command prompt will do the job.
See
How to Alleviate Disk Space Pressure Caused By a Large Windows Component Store (WinSxS) Directory for more info.