Calclus 1.0 calculates lost disk space using diffe
  cluster sizes. Freeware, Win 3.1

  DirSize v2.6   Simon Carter,Crystal Software
  DirSize shows you a graphical tree of the 
  directories on your disk with each's size
  and wasted space, either as a % or value.
  You can control the directory depth that is
  shown. Multi-level directories have summary 
  statistics, very useful for finding the
  complete size of applications before 
  deletion or backup. Displays Windows 95

  FREE 1.1 - Simple utility to report on
  free drive space. FREEWARE of course,
  includes source code!