How To check what files are taking up all the space on your computer with TreeSize

I have to use this occasionally when I lose a lot of space on my hard drive, and don't know why.
TreeSize
http://www.jam-software.com/freeware/index.shtml

Every hard disk is too small if you just wait long enough.
TreeSize Free tells you where precious space has gone to.
TreeSize Free can be started from the context menu of a folder or drive and shows you the size of this folder, including its sub-folders.
You can expand this folder in Explorer-like style and you will see the size of every sub-folder.
Scanning is done in a thread, so you can already see results while TreeSize Free is working.
The space, which is wasted by the file system, can be displayed and the results can be printed in a report.

running on my computer - a very useful program to see where all that space has gone
Give it time to run. There is a tiny status bar at top left that is easy to miss.

Cheers. Si.
Checked for links and relevance, April 2014. Still very relevant for Windows XP and Windows 7
Hmm, I just ran this on my Windows 7 box and to my surprise, I need to delete a couple of massive games I have never played.