TreeSize Free
TreeSize Free tells you where the disk space has gone to. It can be started from the context menu of a folder or drive and shows you the size of this folder, including its subfolders and files. Scanning is done in a thread, so you can see results during the scan. Explorer context menu is supported within TreeSize, as well as the usual drag & drop operations. It now also includes the feature to show the NTFS compression rate. (NTFSRatio)