An interesting software to lock folder: http://www.winability.com/folderguard/

If you don't have a NTFS disk ... can be useful

Treepie applied to the whole Google directory! WOW!
http://www.geocities.com/borgnamarco/Top.html

Visual disk usage [Duv] : http://bitwagon.com/duv/duv.html
Funny: at least has a colorfull display.

For linux

A quite cool and colorfull disk usage tool :

http://www.coolutils.com/SpaceSearcher

cool icon at least :D