This image was generated by the open source OS X application GrandPerspective. It shows how my drive’s capacity is organized. This visual map of a hard drive makes easier for to identify what large files are crowding a hard drive.
The red area is my user data.
The yellow is the Sleep/Swap memory.
The purple blue is System Library.
The turquoise is the Applications.
The sliver of orange is /usr.
Each rectangle represents a file. The bigger the rectangle the larger the file. The large rectangle in the upper left is my Parallels/WindowsXP drive image.
Mousing over any square will show the path to the file. Clicking on the rectangle and then on the reveal button will… surprise, reveal the file in the Finder.
For Windows users there is SpaceMonger. The latest version is $19.95. But the older version, 1.4 is free.