From the list of tools Scott Hanselman calles 2011 Ultimate Developer and Power Users Tool List for Windows I downloaded and installed WinDirStat and used it recently to pinpoint why my disk was allways full.
WinDirStat scans the entire harddisk or only a certain disk and shows the size of the folders. This scanning can take a while so be patient and enjoy the process indicators which are pacmans. When it is finished you end up with the Explorer style grid, a list with filetypes and the space it uses and some nice graphical representation. See below for a screenshot from taken their website.
My problem was with Silverlight temp files (2Gb) that an update of the plugin fixed. Also some MP3 files were hogging up space.
Still running smooth and developing Visual Studio on my 30Gb VHD system.